// Workers AI · dad joke modeWhat did Phi say to its friend? You're irrational.

Phi (Φ, φ, or ϕ) is the 21st letter of the Greek alphabet.

Phi or PHI may also refer to:

Science and technology

Mathematics

• Golden ratio (φ)
• Phi coefficient, a measure of association for two binary variables introduced by Karl Pearson
• Euler's totient function or phi function
• Cyclotomic polynomial ($\Phi _{n}(x)$)
• Integrated information theory (IIT) the symbol of which is φ
• Standard normal distribution, $\Phi (x)$ notating its cumulative distribution function and $\phi (x)$ its probability density function

Physics, chemistry and biology

• Phi meson, in particle physics
• Magnetic flux (Φ)
• Peptide PHI (Peptide histidine isoleucine)
• 6-phospho-3-hexuloisomerase, an enzyme
• Phenyl group (Φ), a functional group in organic chemistry
• Pre-harvest interval
• pH(I), the isoelectric point

Computing

• Xeon Phi, an Intel MIC microprocessor
• Φ (Phi) function, in static single-assignment form compiler design
• Codename for the Nokia Lumia 920
• Phi (language model)

Medicine

• Permanent health insurance, against becoming disabled
• Protected health information, in US law

Other science

• Phi phenomenon, in visual perception
• Krumbein phi scale, for the size of a particle or sediment

Arts and entertainment

• Phi (KinKi Kids album) (2007)
• Phi (Truckfighters album) (2007)
• Sailor Phi, a villain in the Sailor Moon manga
• Phi, a character in the visual novels Zero Escape: Virtue's Last Reward and Zero Escape: Zero Time Dilemma.
• Phi: A Voyage from the Brain to the Soul, a book by Giulio Tononi (2012)
• Phi, a character from Beyblade Burst Turbo, a TV show written by Hiro Morita

Organizations

• Packard Humanities Institute
• Paraprofessional Healthcare Institute, a nonprofit organization based in New York City, US
• Pepco Holdings Inc.
• Petroleum Helicopters International, an American commercial helicopter operator
• Phi, a collegiate secret society at Princeton University
• Philadelphia’s major professional sports teams
  • Philadelphia Eagles of the National Football League
  • Philadelphia 76ers of the National Basketball Association
  • Philadelphia Phillies of Major League Baseball
  • Philadelphia Flyers of the National Hockey League
• Post-Polio Health International
• Prince Henry's Institute of Medical Research, a former research institute in Melbourne, Australia

Other uses

• Voiceless bilabial fricative (IPA symbol: ɸ)
• Phi, a village in Sesant, Cambodia
• Phi, ghosts in Thai culture
• Philippines, IOC country code

See also

• Փ, a letter of the Armenian alphabet
• PHI-base (Pathogen–Host Interaction database)
• Kamen Rider 555 or Masked Rider Φ's