Psi

Psi, PSI or Ψ may refer to:

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

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

 * Psi (parapsychology), psychic or paranormal phenomena
 * Psi hit, parapsychological experimentation term
 * Paranormal Site Investigators, in the UK

Biology and medicine

 * 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

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)

Physics and chemistry

 * Pound per square inch, unit of pressure
 * PSI (computational chemistry), software
 * J/psi meson, subatomic particle
 * Porous silicon
 * 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

 * 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