| Acronym | Definition |
|---|
| PI | Private Investigator |
| pi | [not an acronym] name for Greek symbol representing the ratio of the circumference of a circle to its diameter; approximately 3.1416 |
| PI | Per Inquiry |
| PI | Politically Incorrect |
| PI | Product Information |
| PI | Private Investigations (movie) |
| PI | Process Integration |
| PI | Principal Investigator |
| PI | Public Information |
| PI | Program Improvement |
| PI | Process Improvement |
| PI | Phosphate (Inorganic) |
| PI | Protease Inhibitor |
| PI | Professional Indemnity (insurance coverage) |
| PI | Plant Industry (Commonwealth Scientific and Industrial Research Organisation; Australia) |
| PI | Package Insert (medications) |
| PI | Program Information |
| PI | Piauí (Brazilian state) |
| PI | Post Intelligencer (newspaper, Seattle, Washington) |
| PI | Processing Instruction |
| PI | Punto Informatico |
| PI | Paging (assembly language ASM51 assembler control) |
| PI | Privacy International (human rights group) |
| PI | Pulse Induction |
| PI | Program Instructions |
| PI | Presque Isle (Michigan) |
| PI | Propidium Iodide |
| PI | Proportional-Integral (controller) |
| pI | Isoelectric Point (chemistry) |
| PI | Process Industries |
| PI | Predictive Index |
| PI | Propriedade Intelectual (Intellectual Property, Brazil) |
| PI | Pacific Institute |
| PI | Blood Clotting |
| PI | Parris Island |
| PI | Preliminary Injunction |
| PI | Power Integrations |
| PI | Pass Interference (football) |
| PI | Pandemic Influenza |
| PI | Private Idaho |
| PI | Praktische Informatik (German: Applied Informatics) |
| PI | Primary Immunodeficiency |
| PI | Paedagogisches Institut (Vienna, Austria) |
| PI | Program Integrity |
| PI | Process & Instrumentation |
| PI | Philippine Islands (slang) |
| PI | Parallel Interface |
| PI | Public Intoxication (law enforcement) |
| PI | Position Indicator |
| PI | Pulsatility Index |
| PI | Product Integration |
| PI | Power Interface |
| PI | Product Improvement |
| PI | Profitability Index |
| PI | Program Index |
| PI | Plouffe's Inverter |
| PI | Postinjection |
| PI | Pressure Indicator (industrial control description) |
| PI | Pacific Internet (Internet Service Provider) |
| PI | Post Inoculation |
| PI | Precision Instrument |
| PI | Productivity Index (oil and gas well performance) |
| PI | Paranormal Investigator |
| PI | Provider Independent (IP address space assigned by IANA) |
| PI | Program Identification |
| PI | Proforma Invoice |
| PI | Programmed Instruction |
| PI | Proyectos Industriales |
| PI | Project Identification (number) |
| PI | Prediction Interval |
| PI | Packet Interface |
| PI | Partner Institution |
| PI | Productivity Increase |
| PI | Page Impression (Internet advertising) |
| PI | Product Integrity |
| PI | Priority Inheritance |
| PI | Protocol Interpreter |
| PI | Paper Insulated |
| PI | International Protocol |
| PI | Prison Industry |
| PI | Program Interruption |
| PI | Paranoid Ideation |
| PI | Panicle Initiation |
| PI | Phosphorus Index |
| PI | Par Intérim (French: Deputizing) |
| PI | Parameter Identifier (ITU-T) |
| PI | Istiqlal Party (Independence Party, Morocco) |
| PI | Particular Integral |
| PI | Patente de Invenção (Patent, Brazil) |
| PI | Prime Implicant |
| PI | Primary Injection |
| PI | Projets Individuels |
| PI | Portable Interceptors |
| PI | Primary Investigations |
| PI | Pusat Informasi (Indonesian: Information Center) |
| PI | Précompte Immobilier (French: tax on real estate) |
| PI | Parents for Inclusion |
| PI | Price Integrity |
| PI | Paradigm Infinitum (Singapore) |
| PI | Program Isolation (IBM) |
| PI | Physicist Interface |
| PI | Praendex Incorporated (Wellesley, MA) |
| PI | Principal Insured |
| PI | PrintImage International |
| PI | Parameter Indicator |
| PI | Prospective Internationale |
| PI | Perceptually Impaired |
| PI | Pulse Inverter |
| PI | Perception Immédiate (French) |
| PI | Projector Infantry |
| PI | Parent Initial |
| PI | Psykoterapiinstitut (Stockholm, Sweden) |
| PI | Paducah & Illinois Railroad |
| PI | Procurement Instruction |
| PI | Page Interleaving |
| PI | Psicología Integrada (Portugese) |
| PI | Professional Informant |
| Pi | Ionized Phosphorus |
| PI | Proto-I.jo |
| PI | Pampers Institute (UK) |
| PI | Passive Intercept |
| PI | Profil Infirmier |
| PI | Probationary Instructor |
| PI | Pallidum Internum |
| PI | Passes Intercepted (soccer) |
| PI | Personal Inspection |
| PI | Polynomial Identity (mathematics) |
| PI | Popcorn Institute (Chicago, IL) |
| PI | Plasticity Index |
| PI | Performance Insight (Oracle) |
| PI | Physik Instrumente |
| PI | Plaque Index (oral hygiene) |
| PI | Performance Indicator |
| PI | Point of Inflection (engineering) |
| PI | Poison Ivy |
| PI | Perlite Institute (Staten Island, NY) |
| PI | Peripheral Iridotomy |
| PI | Paperi-Insinöörit (Finnish: Paper Engineers) |
| PI | Platform Initialization (Specification) |
| PI | Physics International |
| PI | Police Interceptor |
| PI | Pursuit Inc. |
| PI | Pinellas (plant; Florida) |
| PI | Personal Identifier |
| PI | Please Inquire |
| PI | Persistently Infected |
| PI | Pearl Islands (Hawaii) |
| PI | Philadelphia Inquirer (newspaper) |
| PI | Policy and International Affairs |
| PI | Plant Integrity |
| PI | Petroleum Institute |
| PI | Planet Internet |
| PI | Paternity Index |
| PI | Per Inch |
| PI | Pinneberg (auto license plate) |
| PI | Perpetual Inventory |
| PI | Perimeter Institute for Theoretical Physics |
| PI | Payload Integrator |
| PI | Penile Implant |
| PI | Performance Improvement |
| PI | Performance Index |
| PI | Periodic Inspection |
| PI | Personal Injury (legal) |
| PI | Photo Interpretation |
| PI | Photo Interpreter |
| PI | Physical Inventory |
| PI | Physically Impaired |
| PI | Pleasure Island (Disney World) |
| PI | Plug In |
| PI | Point Initiating |
| PI | Point of Impact |
| PI | Point of Intersection |
| PI | Policy Issuance (insurance) |
| PI | Polyisocyanurate (rigid foam contruction material) |
| PI | Population Institute |
| PI | Plant Information (real-time software products such as SCADA) |
| PI | Pisa (Tuscany, Italy) |
| PI | Perforated Initials (philately) |
| PI | Personal Investigator (less common) |
| PI | Purchasing Instruction |
| PI | Phase I (clinical studies) |
| PI | PCNA (Proliferating Cell Nuclear Antigen) Labeling Index |
| PI | Pentium I (Intel) |
| PI | Ponderal Index |
| PI | Physician Information |
| PI | PhotoImpact (digital imaging software) |