• Pir (Sufism), a Sufi teacher, spiritual leader
• Pir (Zoroastrianism), a site in Persia, frequently one of the Zoroastrian faith
• Pir of the Britons, legendary king of the Britons
• Pir, Satu Mare, commune in Satu Mare County, Romania

PIR may refer to:
In science:

• Protein Information Resource, a major protein information database and bioinformatics resource
• Partners in Research, a Canadian charity dedicated to bio-medical research
• Parrot Intermediate Representation, part of Parrot virtual machine
• Passive infrared sensor, an often used part of a security system
• Polyisocyanurate, a plastic typically produced as a foam for thermal insulation
• Prosopographia Imperii Romani, an index of all persons mentioned in ancient literature from the Roman Republic to the Roman Empire

In information technology:

• Peak Information Rate
• Public Interest Registry, a not-for-profit corporation responsible for managing the .org top-level domain.
• Public Information Research, a non-profit corporation that maintains Namebase, an online database of citations to influential people
• Private information retrieval, a protocol that allows a user to retrieve an item from a server in possession of a database without revealing which item she is retrieving
• Process Incident Report

In transportation:

• Pierre Regional Airport
• Phoenix International Raceway
• Portland International Raceway

Other:

• Parachute Infantry Regiment
• Post-Implementation Review
• Public Infrastructure Renewal, a ministry of the Government of Ontario
• The Price Is Right (US game show)
• Property Irregularity Report, what is filled out at the baggage claim when a baggage is lost.