Pi

PI may refer to:

Science

• Isoelectric point, the pH at which a particular molecule or surface carries no net electrical charge.
• Parental investment, in evolutionary biology
• Paternity Index, a value used to calculate probability of paternity
• Phosphatidylinositol, a class of lipids
• Pistillata, a gene that influences the development of flowers in the ABC model of flower development
• Plasticity index, a measure of the plasticity of a soil
• Polyimide, a polymer of imide monomers
• Ponderal index, a measure of leanness of a person (similar to body mass index)
• Principal investigator, the lead scientist or engineer for a particular project
• Propidium iodide, a chemical used as a DNA stain
• Protease inhibitor (pharmacology), class of drugs used to treat or prevent infection by viruses, including HIV and Hepatitis C
• Protease inhibitor (biology), molecules that inhibit the function of proteases
• Pulsatility index, a ratio of blood flow rates

Companies and organizations

• Perimeter Institute for Theoretical Physics, a research centre in Ontario, Canada
• Privacy International, a UK-based charity that supports the right to privacy across the world
• Defunct Piedmont Airlines (1948–89) IATA airline code

Political parties

• Partido Independiente or Independent Party, a political party in Uruguay
• Partido Intransigente or Intransigent Party, an Argentine political party
• Partit per la Independència, a political party in Catalonia (Spain) of the 1990s

Professional occupations

• Principal investigator, the lead scientist in a project
• Private investigator, a person who can be hired to undertake investigations

Computing

• Persistent identifier, a long-lasting reference to a digital object
• Processing Instruction, an SGML and XML node type
• Programmed instruction, a technology invented to improve teaching

Other uses

• PI controller, a concept in automation and control engineering
• Pass interference, a foul in American and Canadian gridiron football
• People's Initiative, one of the modes in which the constitution of the Philippines could be amended
• Politically Incorrect (blog), a German political blog
• Seattle Post-Intelligencer or P-I, a newspaper in the United States
• Primitive Instinct, an English rock band formed in 1987
• Profitability index, the ratio of payoff to investment of a proposed project
• Pirot's license plate code
• Pro forma Invoice

See also

• Pi