# Tag (metadata)

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Keyword assigned to information

Not to be confused with [Markup language](/source/Markup_language) or [HTML element](/source/HTML_element) tags, [Hashtag](/source/Hashtag), or [Mention (blogging)](/source/Mention_(blogging)).

A [tag cloud](/source/Tag_cloud) with terms related to [Web 2.0](/source/Web_2.0)

In [information systems](/source/Information_system), a **tag** is a [keyword or term](/source/Index_term) assigned to a piece of information (such as an [Internet bookmark](/source/Bookmark_(World_Wide_Web)), [multimedia](/source/Multimedia), database [record](/source/Record_(computer_science)), or [computer file](/source/Computer_file)). This kind of [metadata](/source/Metadata) helps describe an item and allows it to be found again by browsing or searching.[1] Tags are generally chosen informally and personally by the item's creator or by its viewer, depending on the system, although they may also be chosen from a [controlled vocabulary](/source/Controlled_vocabulary).[2]: 68

Tagging was popularized by [websites](/source/Website) associated with [Web 2.0](/source/Web_2.0) and is an important feature of many Web 2.0 services.[2][3] It is now also part of other [database systems](/source/Database_system), [desktop applications](/source/Desktop_application), and [operating systems](/source/Operating_system).[4]

## Overview

People use tags to aid [classification](/source/Classification_(machine_learning)), mark ownership, note [boundaries](/source/Boundary_critique), and indicate [online identity](/source/Online_identity). Tags may take the form of words, images, or other identifying marks. An analogous example of tags in the physical world is [museum](/source/Museum) object tagging. People were using textual [keywords](/source/Index_term) to [classify information](/source/Document_classification) and objects long before computers. Computer based [search algorithms](/source/Search_algorithm) made the use of such keywords a rapid way of exploring records.

Tagging gained popularity due to the growth of [social bookmarking](/source/Social_bookmarking), [image sharing](/source/Image_sharing), and [social networking](/source/Social_networking) websites.[2] These sites allow users to create and manage labels (or "tags") that categorize content using simple keywords. Websites that include tags often display collections of tags as [tag clouds](/source/Tag_cloud),[a] as do some desktop applications.[b] On websites that aggregate the tags of all users, an individual user's tags can be useful both to them and to the larger community of the website's users.

Tagging systems have sometimes been classified into two kinds: *top-down* and *bottom-up*.[3]: 142[4]: 24 Top-down [taxonomies](/source/Taxonomy_(general)) are created by an authorized group of designers (sometimes in the form of a [controlled vocabulary](/source/Controlled_vocabulary)), whereas bottom-up taxonomies (called [folksonomies](/source/Folksonomy)) are created by all users.[3]: 142 This definition of "top down" and "bottom up" should not be confused with the distinction between a *single hierarchical* [tree structure](/source/Tree_structure) (in which there is one correct way to classify each item) versus *multiple non-hierarchical* [sets](/source/Set_(abstract_data_type)) (in which there are multiple ways to classify an item); the structure of both top-down and bottom-up taxonomies may be either hierarchical, non-hierarchical, or a combination of both.[3]: 142–143 Some researchers and applications have experimented with combining hierarchical and non-hierarchical tagging to aid in information retrieval.[7][8][9] Others are combining top-down and bottom-up tagging,[10] including in some large library catalogs ([OPACs](/source/Online_public_access_catalog)) such as [WorldCat](/source/WorldCat).[11][12]: 74[13][14]

When tags or other taxonomies have further properties (or [semantics](/source/Semantics_(computer_science))) such as [relationships](/source/Relation_(philosophy)) and [attributes](/source/Attribute_(computing)), they constitute an [ontology](/source/Ontology_(information_science)).[3]: 56–62

In folder system a file cannot exist in two or more folders so tag system has been thought more convenient. But transitioning to tag system requires awareness of difference between properties of two systems. In folder system the information of classification is put outside of the file and we can change folder at once. In tag system the information of classification is put inside the file so changing its tag means changing the file and it needs to be saved again and takes time.

Metadata tags as described in this article should not be confused with the use of the word "tag" in some software to refer to an automatically generated [cross-reference](/source/Cross-reference); examples of the latter are *tags tables* in [Emacs](/source/Emacs)[15] and [*smart tags*](/source/Smart_tag_(Microsoft)) in [Microsoft Office](/source/Microsoft_Office).[16]

## History

The use of keywords as part of an identification and classification system long predates computers. [Paper data storage](/source/Paper_data_storage) devices, notably [edge-notched cards](/source/Edge-notched_card), that permitted classification and sorting by multiple criteria were already in use prior to the twentieth century, and [faceted classification](/source/Faceted_classification) has been used by libraries since the 1930s.

In the late 1970s and early 1980s, [Emacs](/source/Emacs), the text editor for [Unix](/source/Unix) systems, offered a companion software program called *Tags* that could automatically build a table of cross-references called a *tags table* that Emacs could use to jump between a [function call](/source/Function_call) and that function's definition.[17] This use of the word "tag" did not refer to metadata tags, but was an early use of the word "tag" in software to refer to a [word index](/source/Index_(publishing)).

[Online databases](/source/Online_database) and early websites deployed keyword tags as a way for publishers to help users find content. In the early days of the [World Wide Web](/source/World_Wide_Web), the keywords [meta element](/source/Meta_element) was used by [web designers](/source/Web_designer) to tell [web search engines](/source/Web_search_engine) what the web page was about, but these keywords were only visible in a web page's [source code](/source/Source_code) and were not modifiable by users.

"A Description of the Equator and Some ØtherLands", collaborative hypercinema portal, produced by documenta X, 1997. User upload page associating user contributed media with the term *Tag*.

In 1997, the collaborative portal "A Description of the Equator and Some ØtherLands" produced by [documenta](/source/Documenta) X, Germany, used the [folksonomic](/source/Folksonomy) term *Tag* for its co-authors and guest authors on its Upload page.[18] In "The Equator" the term *Tag* for user-input was described as an *abstract literal or keyword* to aid the user. However, users defined singular *Tags*, and did not share *Tags* at that point.

In 2003, the [social bookmarking](/source/Social_bookmarking) website [Delicious](/source/Delicious_(website)) provided a way for its users to add "tags" to their bookmarks (as a way to help find them later);[2]: 162 Delicious also provided browseable aggregated views of the bookmarks of all users featuring a particular tag.[19] Within a couple of years, the [photo sharing](/source/Photo_sharing) website [Flickr](/source/Flickr) allowed its users to add their own text tags to each of their pictures, constructing flexible and easy metadata that made the pictures highly searchable.[20] The success of Flickr and the influence of Delicious popularized the concept,[21] and other [social software](/source/Social_software) websites—such as [YouTube](/source/YouTube), [Technorati](/source/Technorati), and [Last.fm](/source/Last.fm)—also implemented tagging.[22] In 2005, the [Atom](/source/Atom_(standard)) web syndication standard provided a "category" element for inserting subject categories into [web feeds](/source/Web_feed), and in 2007 [Tim Bray](/source/Tim_Bray) proposed a "tag" [URN](/source/Uniform_Resource_Name).[23]

## Examples

### Within a blog

Many systems (and other web [content management systems](/source/Content_management_system)) allow authors to add free-form tags to a post, along with (or instead of) placing the post into a predetermined category.[a] For example, a post may display that it has been tagged with baseball and tickets. Each of those tags is usually a [web link](/source/Web_link) leading to an index page listing all of the posts associated with that tag. The blog may have a sidebar listing all the tags in use on that blog, with each tag leading to an index page. To reclassify a post, an author edits its list of tags. All connections between posts are automatically tracked and updated by the blog software; there is no need to relocate the page within a complex hierarchy of categories.

### Within application software

See also: [Tag editor](/source/Tag_editor)

Some [desktop applications](/source/Desktop_application) and [web applications](/source/Web_application) feature their own tagging systems, such as email tagging in [Gmail](/source/Gmail) and [Mozilla Thunderbird](/source/Mozilla_Thunderbird),[12]: 73 bookmark tagging in [Firefox](/source/Firefox),[24] audio tagging in [iTunes](/source/ITunes) or [Winamp](/source/Winamp), and photo tagging in various applications.[25] Some of these applications display collections of tags as [tag clouds](/source/Tag_cloud).[b]

### Assigned to computer files

There are various systems for applying tags to the files in a computer's [file system](/source/File_system).

In [Apple](/source/Apple_Inc.)'s [Mac](/source/Macintosh) [System 7](/source/System_7), released in 1991, users could assign one of [seven editable colored labels](/source/Label_(Mac_OS)) (with editable names such as "Essential", "Hot", and "In Progress") to each file and folder.[26] In later iterations of the Mac operating system ever since [OS X 10.9](/source/OS_X_10.9) was released in 2013, users could assign multiple arbitrary tags as [extended file attributes](/source/Extended_file_attributes) to any file or folder,[27] and before that time the [open-source](/source/Open-source_license) OpenMeta standard provided similar tagging functionality for [Mac OS X](/source/Mac_OS_X).[28]

Several [semantic file systems](/source/Semantic_file_system) that implement tags are available for the [Linux kernel](/source/Linux_kernel), including [Tagsistant](/source/Tagsistant).[29]

[Microsoft Windows](/source/Microsoft_Windows) allows users to set tags only on [Microsoft Office](/source/Microsoft_Office) documents and some kinds of picture files.[30]

[Cross-platform](/source/Cross-platform) file tagging standards include [Extensible Metadata Platform](/source/Extensible_Metadata_Platform) (XMP), an [ISO standard](/source/List_of_International_Organization_for_Standardization_standards) for embedding metadata into popular image, video and document file formats, such as [JPEG](/source/JPEG) and [PDF](/source/PDF), without breaking their readability by applications that do not support XMP.[31] XMP largely supersedes the earlier [IPTC Information Interchange Model](/source/IPTC_Information_Interchange_Model). [Exif](/source/Exif) is a standard that specifies the image and audio [file formats](/source/File_format) used by [digital cameras](/source/Digital_camera), including some metadata tags.[32] [TagSpaces](/source/TagSpaces) is an open-source cross-platform application for tagging files; it inserts tags into the [filename](/source/Filename).[33]

### For an event

An *official tag* is a keyword adopted by events and conferences for participants to use in their web publications, such as blog entries, photos of the event, and presentation slides.[34] Search engines can then index them to make relevant materials related to the event searchable in a uniform way. In this case, the tag is part of a [controlled vocabulary](/source/Controlled_vocabulary).

### In research

A researcher may work with a large collection of items (e.g. press quotes, a bibliography, images) in digital form. If he/she wishes to associate each with a small number of themes (e.g. to chapters of a book, or to sub-themes of the overall subject), then a group of tags for these themes can be attached to each of the items in the larger collection.[35] In this way, freeform [classification](/source/Categorization) allows the author to manage what would otherwise be unwieldy amounts of information.[36]

## Special types

### Triple tags

See also: [Microformat](/source/Microformat)

A **triple tag** or **machine tag** uses a special [syntax](/source/Syntax) to define extra [semantic](/source/Semantic) information about the tag, making it easier or more meaningful for interpretation by a computer program.[37] Triple tags comprise three parts: a [namespace](/source/Namespace), a [predicate](https://en.wiktionary.org/wiki/predicate), and a value. For example, geo:long=50.123456 is a tag for the geographical [longitude](/source/Longitude) coordinate whose value is 50.123456. This triple structure is similar to the [Resource Description Framework](/source/Resource_Description_Framework) model for information.

The triple tag format was first devised for geolicious in November 2004,[38] to map [Delicious](/source/Delicious_(website)) bookmarks, and gained wider acceptance after its adoption by Mappr and GeoBloggers to map [Flickr](/source/Flickr) photos.[39] In January 2007, Aaron Straup Cope at Flickr introduced the term *machine tag* as an alternative name for the triple tag, adding some questions and answers on purpose, syntax, and use.[40]

Specialized metadata for geographical identification is known as *[geotagging](/source/Geotagging)*; machine tags are also used for other purposes, such as identifying photos taken at a specific event or naming species using [binomial nomenclature](/source/Binomial_nomenclature).[41]

### Hashtags

Main article: [Hashtag](/source/Hashtag)

A hashtag is a kind of metadata tag marked by the prefix #, sometimes known as a "hash" symbol. This form of tagging is used on [microblogging](/source/Microblogging) and [social networking services](/source/Social_networking_service) such as [Twitter](/source/Twitter), [Facebook](/source/Facebook), [Google+](/source/Google%2B), [VK](/source/VK_(social_network)) and [Instagram](/source/Instagram). The hash is used to distinguish tag text, as distinct, from other text in the post.

### Knowledge tags

See also: [Knowledge base](/source/Knowledge_base), [Knowledge organization](/source/Knowledge_organization), [Knowledge representation](/source/Knowledge_representation), and [Personal knowledge base](/source/Personal_knowledge_base)

A **knowledge tag** is a type of [meta-information](/source/Metadata) that describes or defines some aspect of a piece of information (such as a [document](/source/Document), [digital image](/source/Digital_image), [database table](/source/Database_table), or [web page](/source/Web_page)).[42] Knowledge tags are more than traditional non-hierarchical [keywords or terms](/source/Index_term); they are a type of [metadata](/source/Metadata) that captures knowledge in the form of descriptions, categorizations, classifications, [semantics](/source/Semantics), comments, notes, annotations, [hyperdata](/source/Hyperdata), [hyperlinks](/source/Hyperlinks), or references that are collected in tag profiles (a kind of [ontology](/source/Ontology_(information_science))).[42] These tag profiles reference an information resource that resides in a distributed, and often heterogeneous, storage repository.[42]

Knowledge tags are part of a [knowledge management](/source/Knowledge_management) discipline that leverages [Enterprise 2.0](/source/Enterprise_2.0) methodologies for users to capture insights, expertise, attributes, dependencies, or relationships associated with a data resource.[3]: 251[43] Different kinds of knowledge can be captured in knowledge tags, including factual knowledge (that found in books and data), conceptual knowledge (found in perspectives and concepts), expectational knowledge (needed to make judgments and hypothesis), and methodological knowledge (derived from reasoning and strategies).[43] These forms of [knowledge](/source/Knowledge) often exist outside the data itself and are derived from personal experience, insight, or expertise. Knowledge tags are considered an expansion of the information itself that adds additional value, context, and meaning to the information. Knowledge tags are valuable for preserving organizational intelligence that is often lost due to [turnover](/source/Turnover_(employment)), for sharing knowledge stored in the minds of individuals that is typically isolated and unharnessed by the organization, and for connecting knowledge that is often lost or disconnected from an information resource.[44]

## Advantages and disadvantages

In a typical tagging system, there is no explicit information about the meaning or [semantics](/source/Semantics) of each tag, and a user can apply new tags to an item as easily as applying older tags.[2] Hierarchical classification systems can be slow to change, and are rooted in the culture and era that created them; in contrast, the flexibility of tagging allows users to classify their collections of items in the ways that they find useful, but the personalized variety of terms can present challenges when searching and browsing.

When users can freely choose tags (creating a [folksonomy](/source/Folksonomy), as opposed to selecting terms from a [controlled vocabulary](/source/Controlled_vocabulary)), the resulting metadata can include [homonyms](/source/Homonym) (the same tags used with different meanings) and [synonyms](/source/Synonym) (multiple tags for the same concept), which may lead to inappropriate connections between items and inefficient searches for information about a subject.[45] For example, the tag "orange" may refer to the [fruit](/source/Orange_(fruit)) or the [color](/source/Orange_(colour)), and items related to a version of the [Linux kernel](/source/Linux_kernel) may be tagged "Linux", "kernel", "Penguin", "software", or a variety of other terms. Users can also choose tags that are different [inflections](/source/Inflection) of words (such as singular and plural),[46] which can contribute to navigation difficulties if the system does not include [stemming](/source/Stemming) of tags when searching or browsing. Larger-scale folksonomies address some of the problems of tagging, in that users of tagging systems tend to notice the current use of "tag terms" within these systems, and thus use existing tags in order to easily form connections to related items. In this way, folksonomies may collectively develop a partial set of tagging conventions.

### Complex system dynamics

Despite the apparent lack of control, research has shown that a simple form of shared vocabulary emerges in social bookmarking systems. Collaborative tagging exhibits a form of [complex systems](/source/Complex_system) dynamics (or [self-organizing](/source/Self-organization) dynamics).[47] Thus, even if no central controlled vocabulary constrains the actions of individual users, the distribution of tags converges over time to stable [power law](/source/Power_law) distributions.[47] Once such stable distributions form, simple [folksonomic](/source/Folksonomy) vocabularies can be extracted by examining the [correlations](/source/Correlation) that form between different tags. In addition, research has suggested that it is easier for [machine learning](/source/Machine_learning) algorithms to learn tag semantics when users tag "verbosely"—when they annotate resources with a wealth of freely associated, descriptive keywords.[48]

### Spamming

Tagging systems open to the public are also open to tag spam, in which people apply an excessive number of tags or unrelated tags to an item (such as a [YouTube](/source/YouTube) video) in order to attract viewers. This abuse can be mitigated using human or statistical identification of spam items.[49] The number of tags allowed may also be limited to reduce spam.

## Syntax

Some tagging systems provide a single [text box](/source/Text_box) to enter tags, so to be able to [tokenize](/source/Tokenize) the string, a [separator](https://en.wiktionary.org/wiki/separator) must be used. Two popular separators are the [space character](/source/Space_(punctuation)) and the [comma](/source/Comma). To enable the use of separators in the tags, a system may allow for higher-level separators (such as [quotation marks](/source/Quotation_mark)) or [escape characters](/source/Escape_character). Systems can avoid the use of separators by allowing only one tag to be added to each input [widget](/source/Web_widget) at a time, although this makes adding multiple tags more time-consuming.

A syntax for use within [HTML](/source/HTML) is to use the **rel-tag** [microformat](/source/Microformat) which uses the [*rel* attribute](/source/Rel_attribute) with value "tag" (i.e., rel="tag") to indicate that the linked-to page acts as a tag for the current context.[50]

## See also

- [Annotation](/source/Annotation)

- [Collective intelligence](/source/Collective_intelligence)

- [Concept map](/source/Concept_map)

- [Enterprise bookmarking](/source/Enterprise_bookmarking)

- [Enterprise social software](/source/Enterprise_social_software)

- [Expert system](/source/Expert_system)

- [Explicit knowledge](/source/Explicit_knowledge)

- [Human–computer interaction](/source/Human%E2%80%93computer_interaction)

- [Information ecology](/source/Information_ecology)

- [Knowledge transfer](/source/Knowledge_transfer)

- [Knowledge worker](/source/Knowledge_worker)

- [Management information system](/source/Management_information_system)

- [Meta-knowledge](/source/Meta-knowledge)

- [Organizational memory](/source/Organizational_memory)

- [RRID](/source/RRID)

- [Semantics](/source/Semantics)

- [Semantic Web](/source/Semantic_Web)

- [Social network aggregation](/source/Social_network_aggregation)

- [Subject (documents)](/source/Subject_(documents))

- [Subject indexing](/source/Subject_indexing)

## Notes

1. ^ [***a***](#cite_ref-Blogs_5-0) [***b***](#cite_ref-Blogs_5-1) For example, [Blogger](/source/Blogger) and [WordPress](/source/WordPress) can display tag clouds.

1. ^ [***a***](#cite_ref-DesktopTagCloud_8-0) [***b***](#cite_ref-DesktopTagCloud_8-1) For example: Leap is a [macOS](/source/MacOS) application that features a clickable tag cloud of macOS tags.[5] TaggTool is a [Windows](/source/Windows) application that permits tagging files and displaying a tag cloud.[6]

## References

1. **[^](#cite_ref-1)** Some users, however, see tags not as metadata but as "just more content": Berendt, Bettina; Hanser, Christoph (2007). ["Tags are not metadata, but 'just more content'—to some people"](http://icwsm.org/papers/2--Berendt-Hanser.pdf) (PDF). *Proceedings of the International Conference on Weblogs and Social Media (ICWSM), Boulder, Colorado, USA, March 26–28, 2007*. Menlo Park, CA: [International Joint Conferences on Artificial Intelligence](/source/International_Joint_Conferences_on_Artificial_Intelligence). [OCLC](/source/OCLC_(identifier)) [799635928](https://search.worldcat.org/oclc/799635928).

1. ^ [***a***](#cite_ref-Smith2008_2-0) [***b***](#cite_ref-Smith2008_2-1) [***c***](#cite_ref-Smith2008_2-2) [***d***](#cite_ref-Smith2008_2-3) [***e***](#cite_ref-Smith2008_2-4) Smith, Gene (2008). [*Tagging: people-powered metadata for the social web*](https://archive.org/details/isbn_9780321529176). Berkeley: [New Riders Press](/source/New_Riders_Press). [ISBN](/source/ISBN_(identifier)) [978-0-321-52917-6](https://en.wikipedia.org/wiki/Special:BookSources/978-0-321-52917-6). [OCLC](/source/OCLC_(identifier)) [154806677](https://search.worldcat.org/oclc/154806677).

1. ^ [***a***](#cite_ref-Breslin-et-al-2009_3-0) [***b***](#cite_ref-Breslin-et-al-2009_3-1) [***c***](#cite_ref-Breslin-et-al-2009_3-2) [***d***](#cite_ref-Breslin-et-al-2009_3-3) [***e***](#cite_ref-Breslin-et-al-2009_3-4) [***f***](#cite_ref-Breslin-et-al-2009_3-5) Breslin, John G.; Passant, Alexandre; Decker, Stefan (2009). *The social semantic web*. Heidelberg; New York: [Springer-Verlag](/source/Springer-Verlag). [doi](/source/Doi_(identifier)):[10.1007/978-3-642-01172-6](https://doi.org/10.1007%2F978-3-642-01172-6). [ISBN](/source/ISBN_(identifier)) [978-3-642-01171-9](https://en.wikipedia.org/wiki/Special:BookSources/978-3-642-01171-9). [OCLC](/source/OCLC_(identifier)) [506401195](https://search.worldcat.org/oclc/506401195).

1. ^ [***a***](#cite_ref-JonesHafner2012_4-0) [***b***](#cite_ref-JonesHafner2012_4-1) Jones, Rodney H.; Hafner, Christoph A. (2012). ["Networks and organization"](https://books.google.com/books?id=-uySkGNM4RAC&pg=PA23). *Understanding digital literacies: a practical introduction*. Milton Park, Abingdon, Oxon; New York: [Routledge](/source/Routledge). pp. 23–28. [ISBN](/source/ISBN_(identifier)) [978-0-415-67316-7](https://en.wikipedia.org/wiki/Special:BookSources/978-0-415-67316-7). [OCLC](/source/OCLC_(identifier)) [711041611](https://search.worldcat.org/oclc/711041611).

1. **[^](#cite_ref-6)** Hampton-Smith, Sam (12 April 2013). ["The pro designer's guide to photo organization"](https://web.archive.org/web/20130416012408/http://www.creativebloq.com/design-tools/organising-your-images-4132310). *creativebloq.com*. Archived from [the original](http://www.creativebloq.com/design-tools/organising-your-images-4132310) on 16 April 2013. Retrieved 10 March 2017. As with all the other options here, meta data can be added to individual files to help improve their find-ability, and uniquely the tag cloud field within Leap's interface allows you to quickly drill down to individually labelled files without fuss.

1. **[^](#cite_ref-7)** Henry, Alan (28 April 2010). ["TaggTool: organize your files by keyword"](https://web.archive.org/web/20150711002811/http://appscout.pcmag.com/utilities/270236-taggtool-organize-your-files-by-keyword). *pcmag.com*. [PC Magazine](/source/PC_Magazine). Archived from [the original](http://appscout.pcmag.com/utilities/270236-taggtool-organize-your-files-by-keyword) on 11 July 2015. Retrieved 10 March 2017.

1. **[^](#cite_ref-9)** Heymann, Paul; Garcia-Molina, Hector (2006). [*Collaborative creation of communal hierarchical taxonomies in social tagging systems*](http://ilpubs.stanford.edu/775/) (Technical report). [Stanford University](/source/Stanford_University). Summarized in: Heymann, Paul (2006). ["Tag hierarchies"](https://web.archive.org/web/20160625094513/http://infolab.stanford.edu/~heymann/taghierarchy.html). *infolab.stanford.edu*. Archived from [the original](http://infolab.stanford.edu/~heymann/taghierarchy.html) on 25 June 2016. Retrieved 10 March 2017.

1. **[^](#cite_ref-10)** Quintarelli, Emanuele; Resmini, Andrea; Rosati, Luca (June 2007). ["Information architecture: Facetag: integrating bottom-up and top-down classification in a social tagging system"](https://doi.org/10.1002%2Fbult.2007.1720330506). *[Bulletin of the American Society for Information Science and Technology](/source/Bulletin_of_the_American_Society_for_Information_Science_and_Technology)*. **33** (5): 10–15. [doi](/source/Doi_(identifier)):[10.1002/bult.2007.1720330506](https://doi.org/10.1002%2Fbult.2007.1720330506). [S2CID](/source/S2CID_(identifier)) [56905311](https://api.semanticscholar.org/CorpusID:56905311).

1. **[^](#cite_ref-11)** Wu, Harris; Zubair, Mohammad; Maly, Kurt (2007). "Collaborative classification of growing collections with evolving facets". *Proceedings of the eighteenth conference on hypertext and hypermedia, Manchester, UK, September 10–12, 2007*. HT '07. New York: [Association for Computing Machinery](/source/Association_for_Computing_Machinery). pp. 167–170. [CiteSeerX](/source/CiteSeerX_(identifier)) [10.1.1.452.44](https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.452.44). [doi](/source/Doi_(identifier)):[10.1145/1286240.1286289](https://doi.org/10.1145%2F1286240.1286289). [ISBN](/source/ISBN_(identifier)) [978-1-59593-820-6](https://en.wikipedia.org/wiki/Special:BookSources/978-1-59593-820-6). [S2CID](/source/S2CID_(identifier)) [18805677](https://api.semanticscholar.org/CorpusID:18805677).

1. **[^](#cite_ref-12)** Carcillo, Franco; Rosati, Luca (2007). "Tags for citizens: integrating top-down and bottom-up classification in the Turin municipality website". In Schuler, Douglas (ed.). *Online communities and social computing: second international conference, OCSC 2007, held as part of HCI International 2007, Beijing, China, July 22–27, 2007: proceedings*. Vol. 4564. Berlin; New York: [Springer-Verlag](/source/Springer-Verlag). pp. 256–264. [doi](/source/Doi_(identifier)):[10.1007/978-3-540-73257-0_29](https://doi.org/10.1007%2F978-3-540-73257-0_29). [ISBN](/source/ISBN_(identifier)) [978-3-540-73256-3](https://en.wikipedia.org/wiki/Special:BookSources/978-3-540-73256-3). [OCLC](/source/OCLC_(identifier)) [184906067](https://search.worldcat.org/oclc/184906067).

1. **[^](#cite_ref-13)** Wilson, Katie (2007). ["OPAC 2.0: next generation online library catalogues ride the Web 2.0 wave!"](https://web.archive.org/web/20170731190742/https://works.bepress.com/katie_wilson/14/). *Online Currents*. **21** (10): 406–413. Archived from [the original](https://works.bepress.com/katie_wilson/14/) on 2017-07-31. Retrieved 2017-03-11.

1. ^ [***a***](#cite_ref-Yee_14-0) [***b***](#cite_ref-Yee_14-1) Yee, Raymond (2008). ["Understanding tagging and folksonomies"](https://books.google.com/books?id=eGdLbRZ5AX0C&pg=PA61). *Pro Web 2.0 mashups: remixing data and Web services*. The expert's voice in Web development. Berkeley: [Apress](/source/Apress). pp. 61–75. [doi](/source/Doi_(identifier)):[10.1007/978-1-4302-0286-8_3](https://doi.org/10.1007%2F978-1-4302-0286-8_3). [ISBN](/source/ISBN_(identifier)) [978-1-59059-858-0](https://en.wikipedia.org/wiki/Special:BookSources/978-1-59059-858-0). [OCLC](/source/OCLC_(identifier)) [148910044](https://search.worldcat.org/oclc/148910044).

1. **[^](#cite_ref-15)** Willey, Eric (2011). ["A cautious partnership: the growing acceptance of folksonomy as a complement to indexing digital images and catalogs"](http://ir.library.illinoisstate.edu/fpml/57/). *Library Student Journal*. Retrieved 10 March 2017.

1. **[^](#cite_ref-16)** Gerolimos, Michalis (January 2013). "Tagging for libraries: a review of the effectiveness of tagging systems for library catalogs". *Journal of Library Metadata*. **13** (1): 36–58. [doi](/source/Doi_(identifier)):[10.1080/19386389.2013.778730](https://doi.org/10.1080%2F19386389.2013.778730). [S2CID](/source/S2CID_(identifier)) [62681953](https://api.semanticscholar.org/CorpusID:62681953).

1. **[^](#cite_ref-17)** Raman, T. V. (1997). *Auditory user interfaces: toward the speaking computer*. Boston: [Kluwer Academic Publishers](/source/Kluwer_Academic_Publishers). p. [107](https://books.google.com/books?id=-_rxBwAAQBAJ&pg=PA107). [doi](/source/Doi_(identifier)):[10.1007/978-1-4615-6225-2](https://doi.org/10.1007%2F978-1-4615-6225-2). [ISBN](/source/ISBN_(identifier)) [978-0-7923-9984-1](https://en.wikipedia.org/wiki/Special:BookSources/978-0-7923-9984-1). [OCLC](/source/OCLC_(identifier)) [37109286](https://search.worldcat.org/oclc/37109286). [S2CID](/source/S2CID_(identifier)) [34186988](https://api.semanticscholar.org/CorpusID:34186988). Calling a function defined in one compilation unit from within another is analogous to cross references in large hypertext documents. By using tags tables, the Emacs environment enables the user to turn program source code into powerful hypertext documents.

1. **[^](#cite_ref-18)** Wempen, Faithe (2010). *Teach yourself visually Microsoft Access 2010*. Indianapolis: [John Wiley & Sons](/source/John_Wiley_%26_Sons). p. [69](https://books.google.com/books?id=RhziOINLvHsC&pg=PA69). [ISBN](/source/ISBN_(identifier)) [978-0-470-57765-3](https://en.wikipedia.org/wiki/Special:BookSources/978-0-470-57765-3). [OCLC](/source/OCLC_(identifier)) [495271168](https://search.worldcat.org/oclc/495271168). You can turn on smart tags for a field to make it easier to cross-reference data between the Access database and Microsoft Outlook (or another personal information and e-mail program) and the Web.

1. **[^](#cite_ref-19)** Meyrowitz, Norman; Dam, Andries (September 1982). ["Interactive Editing Systems: Part II"](https://doi.org/10.1145%2F356887.356890). *ACM Computing Surveys*. **14** (3): 353–415 (366–367). [doi](/source/Doi_(identifier)):[10.1145/356887.356890](https://doi.org/10.1145%2F356887.356890). [S2CID](/source/S2CID_(identifier)) [16977965](https://api.semanticscholar.org/CorpusID:16977965). EMACS is an M.I.T. display editor designed to be 'extensible, customizable, and self-documenting' [...] Another interesting facility for program editing is the TAGS package. The separate program TAGS builds a TAGS table containing the file name and position in that file in which each application program function is defined. This table is loaded into EMACS; specifying the command Meta, *function name* causes EMACS to select the appropriate file and go to the proper function definition within that file.

1. **[^](#cite_ref-20)** ["A Description of the Equator and Some ØtherLands"](https://web.archive.org/web/20010818013629/http://aporee.org/equator/). *aporee.org*. Archived from [the original](http://aporee.org/equator/) on 18 August 2001. Retrieved 10 March 2017.

1. **[^](#cite_ref-21)** See, for example: [Screenshot of tags on del.icio.us](https://www.flickr.com/photos/joshu/765809051/in/set-72157600740166824/) in 2004 and [Screenshot of a tag page on del.icio.us](https://www.flickr.com/photos/joshu/765817375/in/set-72157600740166824/), also in 2004, both published by [Joshua Schachter](/source/Joshua_Schachter) on July 9, 2007.

1. **[^](#cite_ref-22)** Garrett, Jesse James (4 August 2005). ["An Interview with Flickr's Eric Costello"](https://web.archive.org/web/20171018072846/http://www.adaptivepath.org/ideas/e000519/). Archived from [the original](http://adaptivepath.org/ideas/e000519/) on 18 October 2017. Retrieved 21 September 2017. Tags were not in the initial version of Flickr. Stewart Butterfield wanted to add them. He liked the way they worked on del.icio.us, the social bookmarking application. We added very simple tagging functionality, so you could tag your photos, and then look at all your photos with a particular tag, or any one person's photos with a particular tag. Soon thereafter, users started telling us that what was really interesting about tagging was not just how you've tagged your photos, but how the whole Flickr community has been tagging photos. So we started seeing a lot of requests from users to be able to see a global view of the tagscape.

1. **[^](#cite_ref-23)** Mathes, Adam (December 2004). ["Folksonomies: cooperative classification and communication through shared metadata"](https://web.archive.org/web/20170309071911/http://www.adammathes.com/academic/computer-mediated-communication/folksonomies.html). *adammathes.com*. Archived from [the original](http://www.adammathes.com/academic/computer-mediated-communication/folksonomies.html) on 9 March 2017. Retrieved 10 March 2017.

1. **[^](#cite_ref-24)** Gupta, Manish; Li, Rui; Yin, Zhijun; Han, Jiawei (2011). ["An overview of social tagging and applications"](https://books.google.com/books?id=SE2iRgeYYwcC&pg=PA446). In Aggarwal, Charu C. (ed.). *Social network data analytics*. New York: [Springer-Verlag](/source/Springer-Verlag). pp. 447–497. [doi](/source/Doi_(identifier)):[10.1007/978-1-4419-8462-3_16](https://doi.org/10.1007%2F978-1-4419-8462-3_16). [ISBN](/source/ISBN_(identifier)) [978-1-4419-8461-6](https://en.wikipedia.org/wiki/Special:BookSources/978-1-4419-8461-6). [OCLC](/source/OCLC_(identifier)) [709712928](https://search.worldcat.org/oclc/709712928).

1. **[^](#cite_ref-25)** [Bray, Tim](/source/Tim_Bray) (1 February 2007). ["A Uniform Resource Name (URN) namespace for tag metadata"](https://web.archive.org/web/20161105032324/http://www.tbray.org/tmp/tag-urn.html). *tbray.org*. Archived from [the original](https://www.tbray.org/tmp/tag-urn.html) on 5 November 2016. Retrieved 10 March 2017.

1. **[^](#cite_ref-26)** ["Firefox tip: find bookmarks faster with tags"](https://web.archive.org/web/20161012154755/https://blog.mozilla.org/theden/2013/08/26/firefox-tip-find-bookmarks-faster-with-tags/). *blog.mozilla.org*. [Mozilla Foundation](/source/Mozilla_Foundation). 26 August 2013. Archived from [the original](https://blog.mozilla.org/theden/2013/08/26/firefox-tip-find-bookmarks-faster-with-tags/) on 12 October 2016. Retrieved 10 March 2017.

1. **[^](#cite_ref-27)** Hinton, Mark Justice; Obermeier, Barbara; Sahlin, Doug (2010). "Tagging photos". *Editing digital photos for dummies*. Hoboken, NJ: [John Wiley & Sons](/source/John_Wiley_%26_Sons). [ISBN](/source/ISBN_(identifier)) [978-0-470-59145-1](https://en.wikipedia.org/wiki/Special:BookSources/978-0-470-59145-1). [OCLC](/source/OCLC_(identifier)) [606841528](https://search.worldcat.org/oclc/606841528).

1. **[^](#cite_ref-28)** Poole, Lon (1991). ["Labeling items"](https://archive.org/details/macworldguidetos0000pool/page/97). *[Macworld](/source/Macworld) guide to system 7*. San Mateo, Calif.: [IDG Books](/source/IDG_Books). pp. [97–100](https://archive.org/details/macworldguidetos0000pool/page/97). [ISBN](/source/ISBN_(identifier)) [1-878058-16-9](https://en.wikipedia.org/wiki/Special:BookSources/1-878058-16-9). [OCLC](/source/OCLC_(identifier)) [29876799](https://search.worldcat.org/oclc/29876799).

1. **[^](#cite_ref-29)** Siracusa, John (22 October 2013). ["OS X 10.9 Mavericks: The Ars Technica Review: Tags"](https://web.archive.org/web/20170109052357/http://arstechnica.com/apple/2013/10/os-x-10-9/8/). *arstechnica.com*. [Ars Technica](/source/Ars_Technica). Archived from [the original](https://arstechnica.com/apple/2013/10/os-x-10-9/8/) on 9 January 2017. Retrieved 10 March 2013.

1. **[^](#cite_ref-30)** Cherp, Aleh (17 March 2011). ["Tagging"](https://web.archive.org/web/20160430074346/http://macademic.org/2011/03/17/tagging/). *macademic.org*. Academic workflows on a Mac. Archived from [the original](https://macademic.org/2011/03/17/tagging/) on 30 April 2016. Retrieved 10 March 2017.

1. **[^](#cite_ref-31)** ["Extended attributes and tag file systems"](https://web.archive.org/web/20160811104645/http://www.lesbonscomptes.com/pages/tagfs.html). *lesbonscomptes.com*. 2 July 2015. Archived from [the original](https://www.lesbonscomptes.com/pages/tagfs.html) on 11 August 2016. Retrieved 10 March 2017.

1. **[^](#cite_ref-32)** Schultz, Greg (23 March 2011). ["Tag your files for easier searches in Windows 7"](https://web.archive.org/web/20160829073706/http://www.techrepublic.com/blog/windows-and-office/tag-your-files-for-easier-searches-in-windows-7/). *techrepublic.com*. [TechRepublic](/source/TechRepublic). Archived from [the original](https://www.techrepublic.com/blog/windows-and-office/tag-your-files-for-easier-searches-in-windows-7/) on 29 August 2016. Retrieved 10 March 2017.

1. **[^](#cite_ref-33)** Gasiorowski-Denis, Elizabeth (22 March 2012). ["Adobe Extensible Metadata Platform (XMP) becomes an ISO standard"](https://web.archive.org/web/20170310223841/https://www.iso.org/news/2012/03/Ref1525.html). *iso.org*. [International Organization for Standardization](/source/International_Organization_for_Standardization). Archived from [the original](https://www.iso.org/news/2012/03/Ref1525.html) on 10 March 2017. Retrieved 10 March 2017.

1. **[^](#cite_ref-34)** Płoszajski, Grzegorz (2017). ["Metadata in long-term digital preservation"](https://books.google.com/books?id=MJrlDQAAQBAJ&pg=PA15). In Traczyk, Tomasz; Ogryczak, Włodzimierz; Pałka, Piotr; Śliwiński, Tomasz (eds.). *Digital preservation: putting it to work*. Studies in computational intelligence. Vol. 700. New York: [Springer-Verlag](/source/Springer-Verlag). pp. 15–61. [doi](/source/Doi_(identifier)):[10.1007/978-3-319-51801-5_2](https://doi.org/10.1007%2F978-3-319-51801-5_2). [ISBN](/source/ISBN_(identifier)) [978-3-319-51800-8](https://en.wikipedia.org/wiki/Special:BookSources/978-3-319-51800-8). [OCLC](/source/OCLC_(identifier)) [969844731](https://search.worldcat.org/oclc/969844731).

1. **[^](#cite_ref-35)** Devcic, Ivana Isadora (9 October 2015). ["Tag, you're it! How to manage files on Linux with TagSpaces"](https://web.archive.org/web/20161228100443/http://www.makeuseof.com/tag/tag-youre-manage-files-linux-tagspaces/). *makeuseof.com*. MakeUseOf. Archived from [the original](http://www.makeuseof.com/tag/tag-youre-manage-files-linux-tagspaces/) on 28 December 2016. Retrieved 10 March 2017.

1. **[^](#cite_ref-36)** Finch, Curt (26 May 2011). ["Hashtag techniques for businesses"](http://www.inc.com/tech-blog/twitter-hashtag-techniques-for-businesses.html). *inc.com*. [Inc. Magazine](/source/Inc._(magazine)). Retrieved 10 March 2017.

1. **[^](#cite_ref-37)** Parry, David (11 March 2007). ["Tagging files—or how to keep research organized"](https://web.archive.org/web/20160802081239/http://academhack.outsidethetext.com/home/2007/tagging-filesor-how-to-keep-research-organized/). *academhack.outsidethetext.com*. Archived from [the original](http://academhack.outsidethetext.com/home/2007/tagging-filesor-how-to-keep-research-organized/) on 2 August 2016. Retrieved 10 March 2017.

1. **[^](#cite_ref-38)** Smith, Richard (December 2010). ["Strategies for coping with information overload"](http://www.bmj.com/content/341/bmj.c7126). *[The BMJ](/source/The_BMJ)*. **341** c7126. [doi](/source/Doi_(identifier)):[10.1136/bmj.c7126](https://doi.org/10.1136%2Fbmj.c7126). [PMID](/source/PMID_(identifier)) [21159764](https://pubmed.ncbi.nlm.nih.gov/21159764). [S2CID](/source/S2CID_(identifier)) [31128922](https://api.semanticscholar.org/CorpusID:31128922).

1. **[^](#cite_ref-39)** Bainbridge, Scott; Page, Geoff; Jaroensutasinee, Mullica; Jaroensutasinee, Krisanadej (September 2011). ["Towards a services based architecture for real time marine observing data"](https://ieeexplore.ieee.org/document/6106990). *OCEANS '11 MTS/IEEE Kona, Waikoloa, Hawaii, USA, 19–22 22 September 2011*. Piscataway, NJ: [IEEE](/source/IEEE). pp. 740–745. [ISBN](/source/ISBN_(identifier)) [978-1-4577-1427-6](https://en.wikipedia.org/wiki/Special:BookSources/978-1-4577-1427-6). [OCLC](/source/OCLC_(identifier)) [777270556](https://search.worldcat.org/oclc/777270556).

1. **[^](#cite_ref-40)** Maron, Mikel (5 November 2004). ["geo.lici.us: geotagging hosted services"](https://web.archive.org/web/20070428042415/http://brainoff.com/weblog/2004/11/05/124). *brainoff.com*. Archived from [the original](http://brainoff.com/weblog/2004/11/05/124) on 28 April 2007. Retrieved 10 March 2017.

1. **[^](#cite_ref-41)** Catt, Dan (11 January 2006). ["Advanced Tagging and TripleTags"](https://web.archive.org/web/20071011024028/http://geobloggers.com/archives/2006/01/11/advanced-tagging-and-tripletags/). Archived from [the original](http://geobloggers.com/archives/2006/01/11/advanced-tagging-and-tripletags/) on 11 October 2007. Retrieved 10 March 2017.

1. **[^](#cite_ref-42)** Straup Cope, Aaron (24 January 2007). ["Machine tags"](https://web.archive.org/web/20160420154054/https://www.flickr.com/groups/api/discuss/72157594497877875/). *flickr.com*. Archived from [the original](https://www.flickr.com/groups/api/discuss/72157594497877875/) on 20 April 2016. Retrieved 10 March 2017.

1. **[^](#cite_ref-43)** ["The Encyclopedia of Life Flickr group rules"](https://web.archive.org/web/20170210051254/https://www.flickr.com/groups/encyclopedia_of_life/rules/). *flickr.com*. [Encyclopedia of Life](/source/Encyclopedia_of_Life). Archived from [the original](https://www.flickr.com/groups/encyclopedia_of_life/rules/) on 10 February 2017. Retrieved 10 March 2017. Includes the required use of a taxonomy machine tag.

1. ^ [***a***](#cite_ref-Panda-et-al-2012_44-0) [***b***](#cite_ref-Panda-et-al-2012_44-1) [***c***](#cite_ref-Panda-et-al-2012_44-2) Panda, Mrutyunjaya; El-Bendary, Nashwa; Salama, Mostafa A.; Hassanien, Aboul Ella; Abraham, Ajith (2012). ["Computational social networks: tools, perspectives, and challenges"](http://www.softcomputing.net/csn12_chap1.pdf) (PDF). In Abraham, Ajith; Hassanien, Aboul-Ella (eds.). *Computational social networks: tools, perspectives, and applications*. New York: [Springer-Verlag](/source/Springer-Verlag). pp. 3–23 [14–15]. [doi](/source/Doi_(identifier)):[10.1007/978-1-4471-4048-1_1](https://doi.org/10.1007%2F978-1-4471-4048-1_1). [ISBN](/source/ISBN_(identifier)) [978-1-4471-4047-4](https://en.wikipedia.org/wiki/Special:BookSources/978-1-4471-4047-4). [OCLC](/source/OCLC_(identifier)) [798568503](https://search.worldcat.org/oclc/798568503).

1. ^ [***a***](#cite_ref-Wiig_45-0) [***b***](#cite_ref-Wiig_45-1) Wiig, Karl M. (March 1997). "Knowledge management: an introduction and perspective". *[Journal of Knowledge Management](/source/Journal_of_Knowledge_Management)*. **1** (1): 6–14. [doi](/source/Doi_(identifier)):[10.1108/13673279710800682](https://doi.org/10.1108%2F13673279710800682).

1. **[^](#cite_ref-46)** Alavi, Maryam; Leidner, Dorothy E. (February 1999). ["Knowledge management systems: issues, challenges, and benefits"](http://dl.acm.org/citation.cfm?id=374116.374117). *Communications of the AIS*. **1** (2es): 1.

1. **[^](#cite_ref-47)** Golder, Scott A.; Huberman, Bernardo A. (April 2006). "Usage patterns of collaborative tagging systems". *[Journal of Information Science](/source/Journal_of_Information_Science)*. **32** (2): 198–208. [doi](/source/Doi_(identifier)):[10.1177/0165551506062337](https://doi.org/10.1177%2F0165551506062337). [S2CID](/source/S2CID_(identifier)) [1946917](https://api.semanticscholar.org/CorpusID:1946917).

1. **[^](#cite_ref-48)** Devens, Keith (24 December 2004). ["Singular vs. plural tags in a tag-based categorization system (such as del.icio.us)"](https://web.archive.org/web/20120510221217/http://keithdevens.com/weblog/archive/2004/Dec/24/SvP.tags). *keithdevens.com*. Archived from [the original](http://keithdevens.com/weblog/archive/2004/Dec/24/SvP.tags) on 10 May 2012. Retrieved 10 March 2017.

1. ^ [***a***](#cite_ref-WWW07-ref_49-0) [***b***](#cite_ref-WWW07-ref_49-1) Halpin, Harry; Robu, Valentin; Shepherd, Hana (2007). ["The complex dynamics of collaborative tagging"](http://www2007.org/papers/paper635.pdf) (PDF). *Proceedings of the 16th international conference on World Wide Web, Banff, Alberta, Canada, May 08–12, 2007*. WWW '07. New York: [Association for Computing Machinery](/source/Association_for_Computing_Machinery). pp. 211–220. [CiteSeerX](/source/CiteSeerX_(identifier)) [10.1.1.78.5341](https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.78.5341). [doi](/source/Doi_(identifier)):[10.1145/1242572.1242602](https://doi.org/10.1145%2F1242572.1242602). [ISBN](/source/ISBN_(identifier)) [978-1-59593-654-7](https://en.wikipedia.org/wiki/Special:BookSources/978-1-59593-654-7). [OCLC](/source/OCLC_(identifier)) [173331796](https://search.worldcat.org/oclc/173331796). [S2CID](/source/S2CID_(identifier)) [13935265](https://api.semanticscholar.org/CorpusID:13935265).

1. **[^](#cite_ref-50)** Körner, Christian; Benz, Dominik; Hotho, Andreas; Strohmaier, Markus; Stumme, Gerd (2010). ["Stop thinking, start tagging: tag semantics emerge from collaborative verbosity"](http://wwwconference.org/proceedings/www2010/www/p521.pdf) (PDF). [*Proceedings of the 19th International Conference on World Wide Web, Raleigh, North Carolina, USA, April 26–30, 2010*](https://madoc.bib.uni-mannheim.de/61557/). WWW '10. New York: [Association for Computing Machinery](/source/Association_for_Computing_Machinery). pp. 521–530. [doi](/source/Doi_(identifier)):[10.1145/1772690.1772744](https://doi.org/10.1145%2F1772690.1772744). [ISBN](/source/ISBN_(identifier)) [978-1-60558-799-8](https://en.wikipedia.org/wiki/Special:BookSources/978-1-60558-799-8). [OCLC](/source/OCLC_(identifier)) [671101543](https://search.worldcat.org/oclc/671101543). [S2CID](/source/S2CID_(identifier)) [3580366](https://api.semanticscholar.org/CorpusID:3580366).

1. **[^](#cite_ref-51)** Heymann, Paul. ["Tag spam"](http://heymann.stanford.edu/tagspam.html). *stanford.edu*. [Stanford University](/source/Stanford_University). Retrieved 10 March 2017.

1. **[^](#cite_ref-52)** ["Microformats wiki: rel='tag'"](http://microformats.org/wiki/rel-tag). *microformats.org*. 10 January 2005. Retrieved 10 March 2017.

v t e Web syndication History Blogging Podcasting Vlogging Web syndication technology Types Art Bloggernacle Classical music Corporate Dream diary Edublog Electronic journal Fake Family Fashion Food Health Law Lifelog MP3 News Photoblog Police Political Project Reverse Travel Warblog Technology General BitTorrent Feed URI scheme Features Linkback Permalink Ping Pingback Reblogging Refback Rollback Trackback Mechanism Thread Geotagging RSS enclosure Synchronization Memetics Atom feed Data feed Photofeed Product feed RDF feed Web feed RSS GeoRSS MRSS RSS TV Social Inter-process communication Mashup Referencing RSS editor RSS tracking Streaming media Standard OPML RSS Advisory Board Usenet World Wide Web XBEL XOXO Form Audio podcast Enhanced podcast Mobilecast Narrowcasting Peercasting Screencast Slidecasting Videocast Webcomic Webtoon Web series Anonymous blogging Collaborative blog Columnist Instant messaging Liveblogging Microblog Mobile blogging Spam blog Video blogging Motovlogging Media Alternative media Carnivals Fiction Journalism Citizen Database Online diary Search engines Sideblog Software Web directory Micromedia Aggregation News Poll Review Search Video Atom AtomPub Broadcatching Hashtag NewsML 1 G2 Social communication Social software Web Slice Related Blogosphere Escribitionist Glossary of blogging Pay per click Posting style Slashdot effect Spam in blogs Uses of podcasting

---
Adapted from the Wikipedia article [Tag (metadata)](https://en.wikipedia.org/wiki/Tag_(metadata)) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Tag_(metadata)?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.