Psi, PSI or Ψ may refer to:

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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

  • 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

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

  • 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)