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 () Integrated information theory (IIT) the symbol of which is φ Standard normal distribution, notating its cumulative distribution function and 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: ) 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