| P | Peta - Phosphorus | - | Astronomy |
| P | Pico | - | Astronomy |
| P2P | Peer-to-peer (networking) | - | Astronomy |
| P3I OR P?I | PrePlanned Product Improvement | - | Astronomy |
| PA | Panama (ISO 3166 Digram) - Paraguay (FIPS 10-4 Country Code) -Partial Agonist -Pennsylvania (postal Symbol) - Petampere -PolyAmide (Nylon) - Prince Albert Piercing - Public Address (vocal Amplification System) - Public Affairs | - | Astronomy |
| PA | Pascal - Protactinium | - | Astronomy |
| PA | Picoampere | - | Astronomy |
| PA | Punjabi Language (ISO 639-1 Code) | - | Astronomy |
| PA 6 | Nylon 6 (PolyAmide) (similarly For PA 11 | - | Astronomy |
| PAA | Position Area For Artillery | - | Astronomy |
| PAB | Panamean Balboa (ISO 4217 Currency Code) | - | Astronomy |
| PABX | Private Automated Branch EXchange (company Phone System) | - | Astronomy |
| PAC | Pan Africanist Congress -Partial Solar Calibrator - Patriot Advanced Capabilities - Political Action Committee -Primary Auditory Cortex | - | Astronomy |
| PACOM | (U.S.) Pacific Command | - | Astronomy |
| PADI | Professional Association Of Diving Instructors | - | Astronomy |
| PAEK | PolyArylEtherKetone | - | Astronomy |
| PAFC | Plymouth Argyle Football Club | - | Astronomy |
| PAHO | Pan American Health Organization | - | Astronomy |
| PAI | PolyAmide Imide | - | Astronomy |
| PAK | Pakistan (ISO 3166 Trigram) | - | Astronomy |
| PAKISTAN | Punjab | - | Astronomy |
| PAL | Phase Alternating Line (TV Standard) -Philippine Airlines | - | Astronomy |
| PAM | Precision Attack Missile | - | Astronomy |
| PAMELA | Payload For Antimatter Matter Exploration And Light-nuclei Astrophysics | - | Astronomy |
| PAMELA | Pedestrian Accessibility And Movement Environment Laboratory | - | Astronomy |
| PAN | STARRS -Panoramic Survey Telescope And Rapid Response System | - | Astronomy |
| PAN | Panama (ISO 3166 Trigram) -Personal Area Network -PolyAcryloNitrile | - | Astronomy |
| PAN | Punjabi Language (ISO 639-2 Code) | - | Astronomy |
| PANS | Pretty Advanced/Awesome Network Services (cf. POTS) | - | Astronomy |
| PAO | Public Affairs Officer | - | Astronomy |
| PAPI | Precision Approach Path Indicator (aviation) | - | Astronomy |
| PARC | Palo Alto Research Center | - | Astronomy |
| PAROS | Prevention Of An Arms Race In Outer Space (treaty) | - | Astronomy |
| PARP | (NATO Partnership For Peace) Planning And Review Process | - | Astronomy |
| PARWIG | Power Augmented Ram Wing In Ground (aeroplane Wing Shape) | - | Astronomy |
| PAS | See Entry | - | Astronomy |
| PASA | PolyAmide | - | Astronomy |
| PASGT | Personnel Armor System | - | Astronomy |
| PASR | Personnel Accounting And Strength Reporting | - | Astronomy |
| PATH | Port Authority Trans-Hudson | - | Astronomy |
| PAWS | Phased Array Warning System - Progressive Animal Welfare Society | - | Astronomy |
| PAYD | Pay As You Drive | - | Astronomy |
| PAYE | Pay As You Earn | - | Astronomy |
| PB | PolyButylene | - | Astronomy |
| PB | Lead (Latin Plumbum) | - | Astronomy |
| PBB | PolyBrominated Biphenyl | - | Astronomy |
| PBCK | Problem Between Chair And Keyboard (computer Help Desk In-joke) | - | Astronomy |
| PBD | PolyButaDiene | - | Astronomy |
| PBDE | PolyBrominated Diphenyl Ether | - | Astronomy |
| PBI | PolyBenzImidazole | - | Astronomy |
| PBN | PolyButylene Naphthalate | - | Astronomy |
| PBS | Public Broadcasting Service | - | Astronomy |
| PBT | PolyButylene Terephthalate | - | Astronomy |
| PBX | Private Branch EXchange (company Phone System) | - | Astronomy |
| PC | Petacoulomb - U.S. Pacific Islands Trust Territory (ISO 3166 Digram; Obsolete 1986) -Personal Computer - Player Character (roleplaying) - Politically Correct / Political Correctness - Post Cibum (Latin | - | Astronomy |
| PC | Picocoulomb | - | Astronomy |
| PCAS | Planet-Crossing Asteroid Survey | - | Astronomy |
| PCB | See Entry | - | Astronomy |
| PCC | NATO Partnership Coordination Cell - Posterior Cingulate Cortex - Pre-Command Course - Presidents Conference Committee | - | Astronomy |
| PCCB | Porsche Ceramic Composite Brake | - | Astronomy |
| PCCIP | President's Commission On Critical Infrastructure Protection | - | Astronomy |
| PCE | PerChlorEthylene | - | Astronomy |
| PCI | U.S. Pacific Islands Trust Territory (ISO 3166 Trigram; Obsolete 1986) -Peripheral Component Interconnect (computer Bus) | - | Astronomy |
| PCIE | Peripheral Component Interconnect Express (computer Bus) | - | Astronomy |
| PCL | Passive Coherent Location | - | Astronomy |
| PCMCIA | Personal Computer Memory Card International Association (People Can't Memorise Computer-Industry Acronyms) | - | Astronomy |
| PCN | Pitcairn Islands (ISO 3166 Trigram) | - | Astronomy |
| PCP | Phencyclidine - Pneumocystis Jiroveci Pneumonia (formerly Peumocystis Carinii) -Probabilistically Checkable Proof | - | Astronomy |
| PCR | Polymerase Chain Reaction | - | Astronomy |
| PCTE | Portable Common Tool Environment;Punjab College Of Technical Education | - | Astronomy |
| PCZ | Panama Canal Zone (ISO 3166 Trigram; Obsolete 1980) | - | Astronomy |
| PD | Per Diem (Latin: (calculated) By The Day) - Point Of Departure - Police Department - Postal District - Potential Difference - Principal Deputy - Public Domain | - | Astronomy |
| PD | Palladium | - | Astronomy |
| PDA | Personal Digital Assistant - Predicted Drift Angle - Public Display Of Affection - Push-Down Automaton | - | Astronomy |
| PDD | Past Due Date - Presidential Decision Directive | - | Astronomy |
| PDF | Panama[nian] Defense Forces (abolished 1990) - Portable Document Format - Principal Direction Of Fire | - | Astronomy |
| PDG | President Director General - Product Development Group | - | Astronomy |
| PDL | Pure Dumb Luck (Texan Punk Band) | - | Astronomy |
| PDN | Pull-Down Network | - | Astronomy |
| PDQ | Pre-Defined Queries (Siebel Packages) - Pretty Damn Quick | - | Astronomy |
| PDRY | People's Democratic Republic Of Yemen (obsolete Since 1990) | - | Astronomy |
| PDT | Pacific Daylight [Saving] Time (UTC-7 Hours) | - | Astronomy |
| PDU | Police Dog Unit - Power Distribution Unit - Protocol Data Unit | - | Astronomy |
| PE | Ice Pellets (old Style METAR Code) - Peru (ISO 3166 And FIPS 10-4 Country Code Digram) -Physical Education - Premature Ejaculation -Prince Edward Island (postal Code) Price To Earning Ratio (used For Equity Shares) | - | Astronomy |
| PEBCAC | Problem Exists Between Chair And Computer (IT Help Desk In-joke) | - | Astronomy |
| PEBKAC | Problem Exists Between Keyboard And Chair (ditto) | - | Astronomy |
| PEEK | PolyEtherEtherKetone | - | Astronomy |
| PEET | Partnerships For Enhancing Expertise In Taxonomy | - | Astronomy |
| PEI | Prince Edward Island - PolyEtherImide | - | Astronomy |
| PEK | PolyEtherKetone | - | Astronomy |
| PEN | Peruvian Sol (ISO 4217 Currency Code) -PolyEthylene Naphthalate | - | Astronomy |
| PEO | ?…??????… ???…‡??? ???†???‰?… (Greek For Pancyprian Federation Of Labour) - Philanthropic Educational Organization - PolyEthylene Oxide - Professional Employer Organization - Professional Engineers Ontario | - | Astronomy |
| PEPFAR | President's Emergency Plan For AIDS Relief | - | Astronomy |
| PER | Peru (ISO 3166 Trigram) | - | Astronomy |
| PERL | Usually Lower Case Practical Extraction And Report Language | - | Astronomy |
| PES | PolyEtherSulfone | - | Astronomy |
| PEST | UK Public Engagement With Science And Technology | - | Astronomy |
| PET | Personal Electronic Transactor - Pierre Elliott Trudeau - Positron Emission Tomography (as In PET Scan) - PolyEthylene Terephthalate (plastic) -Preliminary English Test | - | Astronomy |
| PETA | Pentaerythritol Triacrylate - People Eating Tasty Animals - People For The Ethical Treatment Of Animals | - | Astronomy |
| PETE | PolyEthyleneTErephthalate | - | Astronomy |
