Psi

{{wiktionary|PSI|Psi|psi}} '''Psi''', '''PSI''' or '''Ψ''' may refer to: <!--Organized per WP:LONGDAB--> {{TOC right}}

==Alphabetic letters== * Psi (Greek) (Ψ or ψ), the twenty-third letter of the Greek alphabet * Psi (Cyrillic), letter of the early Cyrillic alphabet, adopted from Greek

==Arts and entertainment== * "Psi" as an abbreviation for psionics

===Comics=== * Psi (comics), DC Comics character * Psi Division, division in the ''Judge Dredd'' and ''2000 AD'' series of comics * ''Psi-Force'', comic series * Psi-Hawk, comic character * ''Psi Lords'', comic series

===Music=== * ''PSI'' (album), album by Pitchshifter (2002) * Psi Com, 1980s rock band * Psi Power, song by rock group Hawkwind (1978) * Psi Records, music record label * PSI Records, music record label * Ψ CMX DVD, Finnish language video album by the band CMX * ''Pitch Shifter Industries'', acronym used by the British band Pitchshifter * Logo used by the band Twenty One Pilots during their ''Scaled and Icy'' (2021) album era

===Other uses in arts and entertainment=== * ''Psi'' (TV series), Brazil * Psi Corps, in the ''Babylon 5'' fictional universe * ''Psi Factor: Chronicles of the Paranormal'', Canadian television series * ''Psi-Ops: The Mindgate Conspiracy'', 2004 video game

==Organizations==

===Government and politics=== * Italian Socialist Party (''Partito Socialista Italiano''), socialist and later social-democratic political party in Italy * Italian Socialist Party (2007), social-democratic political party in Italy * Indonesian Solidarity Party (''Partai Solidaritas Indonesia'') * Indonesian Socialist Party (''Partai Sosialis Indonesia'') * Proliferation Security Initiative, against weapons technology transfer * ''Public Sector Information'', as in: ** The 2003 EU Directive on the re-use of public sector information ** The UK Office of Public Sector Information (OPSI), formerly HMSO * United States Senate Homeland Security Permanent Subcommittee on Investigations

===Other organizations=== * Paul Scherrer Institute, research institute in Villigen, Switzerland * Pechersk School International, Kyiv, Ukraine * Physics Society of Iran * Planetary Science Institute, Tucson, Arizona, US * Poetry Slam, Inc., promoting poetry * Policy Studies Institute, UK research organization * Population Services International, global health organization * Professional Skills Institute, technical school in Maumee, Ohio, US * Prudential Securities Incorporated, financial services company * PSI Seminars, on awareness training * Public Services International, trades unions federation * Statisticians in the Pharmaceutical Industry

== Parapsychology == {{For|mainstream psychology|#Psychology}} * Psi (parapsychology), psychic or paranormal phenomena * Psi hit, parapsychological experimentation term * Paranormal Site Investigators, in the UK

==Science, technology, and mathematics==

===Biology and medicine=== {{for|psychology|#Psychology}} * PSI (prion), infectious protein in yeast * Pandemic severity index, former US CDC influenza scale * Photosystem I, protein complex involved in photosynthesis * Pneumonia severity index * Protein Structure Initiative, of the U.S. NIGMS

===Computing=== * Psi (instant messaging client), XMPP client program * Potentially Shippable Increment, in the Scrum software development methodology * Program-specific information, part of the MPEG transport stream protocol * Pressure stall information, a Linux kernel patch for out of memory management

=== Cryptography ===

* Private set intersection, a cryptographic technique to compute the intersection of two encrypted sets

===Economics=== * PSI-20, Lisbon, Portugal stock market index * Private sector involvement, in sovereign debt crisis resolution

===Engineering=== * "Yaw" angle, one of the Euler angles, denoted ψ in aerospace engineering *Present serviceability index, a pavement performance indicator introduced by AASHTO

===Geography=== * Psi Islands, in the Melchior Islands, Antarctica ===Mathematics=== * Chebyshev function * Dedekind psi function * Digamma function * Polygamma functions * Stream function, in two-dimensional flows * Polar tangential angle of a curve * Probability of ultimate ruin, in ruin theory * Supergolden ratio *Reciprocal Fibonacci constant * Population Stability Index (Kullback–Leibler divergence#Symmetrised divergence)

===Physics and chemistry=== * Pound per square inch, unit of pressure * PSI (computational chemistry), software * J/psi meson, subatomic particle * Porous silicon ("PS" or "pSi"), a form of silicon with introduced nanopores in its microstructure * Water potential, denoted Ψ, in physical chemistry, the potential energy of a water solution relative to pure water * Wave function, denoted ψ, in quantum mechanics

===Psychology=== {{for|paranormal phenomena|#Parapsychology}} * Psychology or psychologist, denoted Ψ, used in the logo of various psychological associations * Psi Chi, the National Honor Society in psychology * Psi-theory, theory about the human mind, a cognitive architecture * Psychiatric Solutions, Inc., corporation that owns psychiatric hospitals

==Other uses== * Parasocial interaction, non-reciprocal interactions, as between a fanbase and a performer * Permanent staff instructor, in the British Army * Personalized System of Instruction * Pollutant Standards Index, air pollution measure * Pre-shipment inspection, method of quality control * Presentence investigation report, investigation into the history of person convicted of a crime * Proto-Siouan language, the reconstructed ancestor of the Siouan languages

==See also== * Psy (disambiguation) * PS1 (disambiguation)

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