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
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), 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
Other uses in arts and entertainment Psionics, a science fiction concept
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) Pharmaceutical Society of Ireland 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
Science, technology, and mathematics
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
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
Places 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
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 (PSi), the reconstructed ancestor of the Western Siouan languages
See also Psy (disambiguation) PS1 (disambiguation)