Psi

Psi or PSI may refer to:

Alphabetic letters

• Psi (Greek) (Ψ, ψ) 23rd letter of the Greek alphabet
• Psi (Cyrillic) (Ѱ, ѱ), a letter of the early Cyrillic alphabet, adopted from Greek

Mathematics

• Tangential angle of a curve
• Chebyshev function
• Dedekind psi function
• Digamma function
• Polygamma functions
• Stream function, in two-dimensional flows

Mind related

• Psychology or psychologist, denoted Ψ, used in the logo of various psychological associations
• Psi Chi, the National Honor Society in Psychology
• Psi-Theory, a theory about the human mind, a cognitive architecture

• Psi (parapsychology), psychic or paranormal phenomena
• Psi hit, a parapsychological experimentation term
• Paranormal Site Investigators, an education and research charity in the UK

Natural science and technology

• PSI (computational chemistry), software
• PSI (prion), an infectious protein in yeast
• Psi (instant messaging client), a popular XMPP client program
• Pandemic Severity Index, by the US Centers for Disease Control and Prevention
• Pounds per square inch, a unit of pressure
• Photosystem I, a protein complex involved in photosynthesis
• Pneumonia severity index
• Pollutant Standards Index, an air pollution measure
• Porous silicon, a material
• Program Specific Information, part of the MPEG transport stream protocol
• Protocol for Stage Illumination, a communications protocol geared towards stage lighting and effects control
• Protein Structure Initiative, a structural genomics initiative of the U.S. NIGMS
• J/ψ meson, a subatomic particle
• 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
• 'Yaw' angle, denoted ψ in aerospace engineering, the rotation angle of a vehicle around the vertical axis with the Tait-Bryan convention

Organizations

• Paul Scherrer Institute in Villigen, Switzerland
• Poetry Slam, Inc.
• Policy Studies Institute, a UK organization affiliated with the University of Westminster which undertakes research in matters pertaining to work and social policy and the environment
• Population Services International, an international healthcare NGO based in Washington DC
• Professional Secretaries International
• Professors for a Strong Israel, a right-wing group of academics in Israel
• Psychiatric Solutions, Inc., a corporation that owns psychiatric hospitals
• Public Services International, a global union federation of public sector trade unions
• Statisticians in the Pharmaceutical Industry
• PSI, Contract Research Organization (Pharmaceutical Industry)

Entertainment

• Psi (comics), a character in DC Comics
• Psi Com, a 1980s rock band
• Psi Corps, in the Babylon 5 fictional universe, the ruling body of Earth's telepaths
• Psi Division, a division in the Judge Dredd and 2000 AD series of comics
• Psi Factor: Chronicles of the Paranormal, a Canadian television series
• Psi-Force, a comic series
• Psi-Hawk, a comic character
• Psi Lords, a comic series
• Psi-Ops: The Mindgate Conspiracy, a video game in which characters use psychic powers
• Psi Power, a 1978 song by the UK rock group Hawkwind
• PSI, the psychic power used by some characters in the EarthBound series
• PSI (album), an album by Pitchshifter
• PSI Records, a music record label

Politics and government

• Partai Sosialis Indonesia ("Indonesian Socialist Party")
• Italian Socialist Party (Partito Socialista Italiano)
• Italian Socialist Party (2007)
• United States Senate Homeland Security Permanent Subcommittee on Investigations, a sub-committee of the U.S. Senate
• Proliferation Security Initiative, an international effort to interdict transfer of banned weapons and weapons technology
• Public Sector Information, as in
  • The European Union Directive on the re-use of public sector information (PSI directive), adopted in November 2003
  • The United Kingdom's Office of Public Sector Information (OPSI), formerly Her Majesty's Stationary Office (HMSO)

Finance

• PSI, acronym for Private Sector Involvement in sovereign debt restructuring deals, as opposed to OSI, Official Sector Involvement.

Miscellaneous

• Pechersk School International, in Kiev, Ukraine
• Permanent Staff Instructor, in the British Army
• PSI-20, a stock market index of companies that trade on Euronext Lisbon, the main stock exchange of Portugal
• Presentence investigation, in law, an investigation into the history of person convicted of a crime, before sentencing
• Pre-shipment inspection, a method of quality control
• Professional Skills Institute, a private university in Toledo, Ohio
• Pitch Shifter Industries, an acronym used by the British band Pitchshifter