| OPIS | Orbiter Prime Item Specification | In English | → Spaceflight engineering, astronautics |
| OPK | Ovulation Predictor Kit | In English | → Gynaecology → Reproductive biology |
| OPL | Orbiter Project Parts List | In English | → Spaceflight engineering, astronautics |
| OPLF | Orbiter Processing and Landing Facility | In English | → Spaceflight engineering, astronautics |
| OPM | Outer Planet Mission | In English | → Astronomy → Spaceflight engineering, astronautics |
| OPO | Orbiter Project Office | In English | → Spaceflight engineering, astronautics |
| OPOV | Oxidizer Preburner Oxidizer Valve | In English | → Vehicle engineering |
| OPPAR | Orbiter Project Parts Authorization Request | In English | → Spaceflight engineering, astronautics |
| OPPBTP | Organisme Professionnel de Prévention du Bâtiment et des Travaux Publics (www.oppbtp.fr) | In French | → Organizations and associations → Labour, labour economics → Medicine → Civil engineering → Building |
| OPPBTP | Organisme Professionnel de la Prévention du Bâtiment Travaux Publics | In French | → Organizations and associations → Civil engineering → Building |
| OPPTIC | Organisation de Professionnels pour la Promotion des TIC en région Languedoc-Roussillon | In French | → Networks, communication → Organizations and associations → Telecommunications |
| OPQCM | Office Professionnel de Qualification des Conseils en Management | In French | → 6592 |
| OPR | Orbiter Payload Recorder | In English | → Spaceflight engineering, astronautics |
| OPRI | Office de Protection contre les Rayonnements Ionisants | In French | → Nuclear technology |
| OPS | Organización Panamericana de la Salud (www.paho.org) = PAHO | Pan American Health Organization | In English = OPAS | Organização Pan-Americana da Saúde | In Portuguese |
In Spanish | → Organizations and associations → International relations → Medicine |
| OPS | Orbiter Project Schedule | In English | → Spaceflight engineering, astronautics |
| OPSIS | Observation et Prospective sur la Société de l'Information et ses Services | In French | → Computer science → Telecommunications |
| OPSS | Orbital Propellant Storage Subsystem | In English | → Spaceflight engineering, astronautics |
| OptCo | Optics Communications | In English | → Serial publications, periodicals → Optics → Telecommunications |
| OptFT | Optical Fiber Technology | In English | → Serial publications, periodicals → Optics → Telecommunications |
| OPTI | Observatorio de Prospectiva Tecnológica Industrial | In Spanish | → Engineering, technology |
| OptMa | Optical Materials | In English | → Serial publications, periodicals → Optics → 620 |
| OptQE | Optical Quantum Electronics | In English | → Serial publications, periodicals → 530145 → Optics → Engineering, technology |
| OPWC | Organisation for the Prohibition of Chemical Weapons (www.opcw.org) = OIAC | Organisation pour l'Interdiction des Armes Chimiques | In French |
In English | → Organizations and associations → International relations → Military engineering |
| OPWS | Orbital Payload Work Station | In English | → Spaceflight engineering, astronautics |
| OQE | Optical and Quantum Electronics | In English | → Serial publications, periodicals → 530145 → Optics → Engineering, technology |
| ORCUS | Orbital Recording Capability and Update System | In English | → Spaceflight engineering, astronautics |
| ORD | Orbital Requirements Document | In English | → Spaceflight engineering, astronautics |
| ORD | Office of Rare Diseases (http://rarediseases.info.nih.gov) | In English | → 345 → Pathology |
| ORE | Opérateur de Réseau Électricité | In French | → Electrical engineering |
| ORF | Österreichische Rundfunk (http://orf.at) | In German | → Telecommunications |
| ORF | Österreichischer Rundfunk | In German | → Telecommunications |
| ÖRG | Österreichische Röntgengesellschaft | In German | → Organizations and associations → Medicine |
| ORM | Operational Reactivity Margin | In English | → 53912 → Nuclear technology |
| ÖRPE | Österreichische Referenzzentrum zur Erfassung und Dokumentation von menschlichen Prionenerkrankungen | In German | → Pathology |
| ORPHEM | Organisation Régionale des Pharmaciens Hospitaliers de l'Est Méditerranéen | In French | → Organizations and associations → Pharmacology, toxicology |
| ORS | Orbital Resupply System | In English | → Spaceflight engineering, astronautics |
| ORS | Orbital Reservicing System | In English | → Spaceflight engineering, astronautics |
| ORS | Orbital Refueling System | In English | → Spaceflight engineering, astronautics |
| ORS | Österreichische Rundfunksender (www.ors.at) | In German | → Telecommunications |
| ORS | Outer Root Sheath | In English | → Anatomy |
| ORT | Orbit Readiness Test | In English | → Spaceflight engineering, astronautics |
| ORTA | Organisme de Ràdio i Televisió d’Andorra | In Catalan | → Telecommunications |
| ORTAS | Organisme de la Radio-Télévision Arabe Syrienne | In French | → Telecommunications |
| ORU | Orbital Replaceable Unit | In English | → Spaceflight engineering, astronautics |
| ORU | Orbital Replacement Unit | In English | → Spaceflight engineering, astronautics |
| ORV | Orbital Research Vehicle | In English | → Spaceflight engineering, astronautics |
| OS | Orbiter CEI Specification | In English | → Spaceflight engineering, astronautics |
| OS | On-orbit Station | In English | → Spaceflight engineering, astronautics |
| OSB | Orientated Strand Board | In English | → Timber and woodworking industry |
| OSC | Orbital Sciences Corporation | In English | → Spaceflight engineering, astronautics |
| OSCAR | Orbiting Satellite Carrying Amateur Radio | In English | → Spaceflight engineering, astronautics → Telecommunications |
| OsCar | Osteoarthritis and Cartilage | In English | → Serial publications, periodicals → Medicine |
| OSCN | Orbiter Specification Change Notice | In English | → Spaceflight engineering, astronautics |
| OSCR | Orbiter Software Change Request | In English | → Software → Spaceflight engineering, astronautics |
| OSCRS | Orbital Spacecraft Consumables Resupply System | In English | → Maintenance and logistics → Spaceflight engineering, astronautics |
| OSD | Office of the Secretary of Defense | In English | → 355 → Military engineering |
| OSDH | Orbiter System Definition Handbook | In English | → Spaceflight engineering, astronautics |
| OSE | Orbital Support Equipment | In English | → Spaceflight engineering, astronautics |
| OSF | Orbiter Simulation Facility | In English | → Spaceflight engineering, astronautics |
| ÖSG | Österreichische Schmerzgesellschaft | In German | → Organizations and associations → Pathology |
| OSGE | Observatoire Statistique du Groupe EDF | In French | → Electrical engineering |
| OSHA | Occupational Safety and Health Act | In English | → Labour, labour economics → Medicine |
| OSHA | Occupational Safety and Health Administration | In English | → Labour, labour economics → Public administration, government → Medicine |
| OSM | On-Orbit Spares Model | In English | → Spaceflight engineering, astronautics |
| OSM | Orbiter Service Module | In English | → Spaceflight engineering, astronautics |
| OSO | Orbiting Solar Observatory | In English | → Observatories → Spaceflight engineering, astronautics |
| OSOP | Orbiter Systems Operating Procedure | In English | → Spaceflight engineering, astronautics |
| OSR | Oberster Sanitätsrat | In German | → Organizations and associations → Public health and hygiene |
| OSS | Orbiting Space Station | In English | → Spaceflight engineering, astronautics |
| OSS | Office of Space Sciences | In English | → Astronomy → Spaceflight engineering, astronautics |
| OSSA | Office of Space Sciences and Applications | In English | → Astronomy → Spaceflight engineering, astronautics |
| OSSA | Office of Space Science and Applications | In English | → Astronomy → Spaceflight engineering, astronautics |
| OSSIU | Orbiter-Space Station Interface Unit | In English | → Spaceflight engineering, astronautics |
| OSSRH | Orbiter Subsystem Requirements Handbook | In English | → Spaceflight engineering, astronautics |
| OST | Orbiter Support Trolley | In English | → Spaceflight engineering, astronautics |
| OST | Office of the Secretary of Transportation | In English | → Central administration → Transport and postal services |
| OSTA | Office of Space and Terrestrial Applications | In English | → Astronomy → Spaceflight engineering, astronautics |
| OSTDS | Office of Space Tracking and Data Systems | In English | → Data → Spaceflight engineering, astronautics |
| OSTO | Office of Space Transportation Operations | In English | → Spaceflight engineering, astronautics |
| OSTP | Orbiting System Test Plan | In English | → Spaceflight engineering, astronautics |
| OSTP | Office of Science and Technology Policy | In English | → Research policy → Engineering, technology |
| OSTS | Office of Space Transportation Systems | In English | → Spaceflight engineering, astronautics |
| OT | Occupational Therapy | In English | → Labour, labour economics → Medicine |
| OT | Organisation Todt | In French | → Military engineering → History |
| OTA | Operational Trajectory Analysis | In English | → Aeronautics, aircraft → Spaceflight engineering, astronautics |
| OTB | Orbiting Tanker Base | In English | → Spaceflight engineering, astronautics |
| OTC | Orbiter Test Conductor | In English | → Spaceflight engineering, astronautics |
| OTC | Over the Counter | In English | → Pharmacology, toxicology |
| OTD | Operational Technical Documentation | In English | → Engineering, technology |
| OTD | Orbiter Test Director | In English | → Spaceflight engineering, astronautics |
| OTE | Orbital Transfer Equipment | In English | → Spaceflight engineering, astronautics |
| ÖTI | Österreichisches Textil-Forschungsinstitut | In German | → Research institutes → Textile industry |
| OTL | Office of Technology Licensing | In English | → Engineering, technology |
| OTLC | Orbiter Time Line Constraint | In English | → Spaceflight engineering, astronautics |
| OTOS | Orbit-To-Orbit Stage | In English | → Spaceflight engineering, astronautics |
| OTP | Operational Test Procedure | In English | → Engineering, technology |
| OTP | Operations Turnaround Plan | In English | → Engineering, technology |
| OTS | Orbital/Orbital Transfer System | In English | → Spaceflight engineering, astronautics |
| OTS | Orbital Test System | In English | → Spaceflight engineering, astronautics |
| OTV | Operational Television | In English | → Telecommunications |
| OTV | Orbit Test Vehicle | In English | → Spaceflight engineering, astronautics |
| OTV | Orbital Transfer Vehicle | In English | → Spaceflight engineering, astronautics |
| OUP | Oxford University Press | In English | → Higher education, universities → Graphic industries, printing, publishing |
| OUT | Orbiter Utility Tray | In English | → Spaceflight engineering, astronautics |
| OV | Orbiter Vehicle | In English | → Spaceflight engineering, astronautics |
| OV | Orbital Vehicle | In English | → Spaceflight engineering, astronautics |
| OVCAD | OVarian CAncer Diagnosis | In English | → Diagnostics → Oncology → Gynaecology |
| OVCO | Operational Voice Communication Office | In English | → Telecommunications |
| OVEI | Orbiter Vehicle End Item | In English | → Spaceflight engineering, astronautics |
| ÖVG | Österreichische Verkehrswissenschaftlichen Gesellschaft | In German | → Transport and postal services |
| OVI | Operational Validation Inspection | In English | → Management → Engineering, technology |
| ÖVK | Österreichischer Verein für Kraftfahrzeugtechnik (www.?vk.at) | In German | → Organizations and associations → Mechanical engineering |
| ÖVN | Österreichischer Verein für Navigation = AIN | Austrian Institute of Navigation | In English |
In German | → Geodesy, cartography → Vehicle engineering → Transport and postal services |
| OVNI | Oggetto Volante Non Identificato = OVNI | Objet Volant Non Identifié | In French = OVNI | Objecte Volador No Identificat | In Catalan = НЛО | Неидентифициран летящ обект | In Bulgarian = OVNI | Objeto Volador No Identificado | In Spanish = UFO | Unidentifiziertes Flugobjekt | In German = UFO | Unidentified Flying Object | In English = UFO | Unknown Flying Object | In English = UFO | Uidentificeret flyvende objekt | In Danish = NIFO | Neidentigita Fluganta Objekto | In Esperanto = UFO | Unbekend fleanend objekt | In Frisian = עב"מ | עצם בלתי מזוהה | In Hebrew = NLO | Neidentificēts lidojošs objekts | In Latvian = UFO | Uidentifisert flygende objekt | In Norwegian = UFO | Uidentifisert flygande objekt | In Nynorsk = NOL | Niezidentyfikowany Obiekt Latający | In Polish = OVNI | Objeto Voador Não Identificado | In Portuguese = OZN | Obiect Zburător Neidentificat | In Romanian = НЛО | Неопознанный летающий объект | In Russian = NLO | Neidentifikovani leteći objekat | In Serbo-Croatian |
In Italian | → Spaceflight engineering, astronautics |
| OVNI | Objeto Volador No Identificado = НЛО, UFO, NIFO, עב"מ, NLO, NOL, OZN (look above) |
In Spanish | → Spaceflight engineering, astronautics |
| OVNI | Objeto Voador Não Identificado = НЛО, UFO, NIFO, עב"מ, NLO, NOL, OZN (look above) |
In Portuguese | → Spaceflight engineering, astronautics |
| OVNI | Objecte Volador No Identificat = НЛО, UFO, NIFO, עב"מ, NLO, NOL, OZN (look above) |
In Catalan | → Spaceflight engineering, astronautics |
| OVNI | Objet Volant Non Identifié = НЛО, UFO, NIFO, עב"מ, NLO, NOL, OZN (look above) |
In French | → Spaceflight engineering, astronautics |
| OWF | Optimum Working Frequency | In English | → Telecommunications |
| OXCs | Optical cross connects | In English | → Telecommunications |
| OxM | Oxidation of Metals | In English | → Serial publications, periodicals → Chemistry → Metallurgy |
| OZN | Obiect Zburător Neidentificat = OVNI, НЛО, UFO, NIFO, עב"מ, NLO, NOL (look above) |
In Romanian | → Spaceflight engineering, astronautics |
| P&D | Pesquisa e Desenvolvimento = R&D | Recherche et développement | In French = F&E | Forschung und Entwicklung | In German = R&D | Research and Development | In English = I+D | Investigación y Desarrollo | In Spanish = R&S | Ricerca e Sviluppo | In Italian = O&O | Onderzoek en Ontwikkeling | In Dutch = FoU | Forsøk og Utvikling | In Norwegian |
In Portuguese | → Research policy → Engineering, technology |
| P&E | Propellant and Explosive | In English | → Spaceflight engineering, astronautics → Chemical technology |
| P&T | Post en Telegraaf | In Dutch | → Telecommunications → Transport and postal services |
| P&TE | Packaging and Transport Engineering | In English | → Transport and postal services |
| P&VE | Propulsion and Vehicle Engineering | In English | → Vehicle engineering |
| P-HUS | Pneumococcal-associated Hemolytic Uremic Syndrome | In English | → Blood and circulatory system → Pathology |
| P3P | Platform for Privacy Preferences | In English | → Networks, communication → Telecommunications |
| P3S | Power Systems Supports and Services | In English | → Electrical engineering |
| PA | Petites Annonces | In French | → Graphic industries, printing, publishing |
| PA | Polyamide | In English | → Plastic industry → Chemicals → Chemistry |
| PAA | Pan American Airlines | In English | → Transport and postal services |
| PAA | Population Active Agricole | In French | → Agricultural sciences |
| PAAR | Professional Association of Andrologists of Russia | In English | → Associations → Sexual problems → Urology |
| PAC | Pile à combustible | In French | → Energy economics → Electrical engineering |
| PACE | Power and Control Electronics | In English | → Electronics |
| PACE | Prelaunch Automatic Checkout Equipment | In English | → Vehicle engineering |
| PACO | Prelaunch Automatic Checkout | In English | → Vehicle engineering |
| PACRUSS | Passive and Active Control of Space Structures | In English | → Spaceflight engineering, astronautics |
| PACS | Pointing and Attitude Control System | In English | → Spaceflight engineering, astronautics |
| PAD | Propellant Acquisition Device | In English | → Spaceflight engineering, astronautics |
| PADSIM | Precision Attitude Determination Simulation | In English | → Spaceflight engineering, astronautics |
| PAE | Pulmonale arterielle Hypertonie | In German | → Blood and circulatory system → Chest diseases |
| PAF | Penicillium AntiFungal protein | In English | → Biochemistry, biophysics → Agricultural sciences |
| PAF | Penicillium Antifungal (protein) | In English | → Biochemistry, biophysics → Pharmacology, toxicology |
| PAFB | Patrick Air Force Base | In English | → 358 → Aeronautics, aircraft |
| PAH | Pulmonal arterielle Hypertonie | In German | → Pathology |
| PAH | Port Autonome du Havre | In French | → Transport and postal services |
| PAHO | Pan American Health Organization (www.paho.org) = OPS, OPAS (look above) |
In English | → Organizations and associations → International relations → Medicine |
| PAI | Plasminogen Activator Inhibitor | In English | → Enzymes → Blood and circulatory system |
| PAL | Phosphatase Alcaline Leucocytaire | In French | → Enzymes → Blood and circulatory system |
| PAL | Phase Alternated Line | In English | → Telecommunications |
| PALH | Physician Assistant for Latino Health | In English | → Organizations and associations → Medicine → International relations |
| PALS | Precision Approach and Landing System | In English | → Aeronautics, aircraft → Spaceflight engineering, astronautics |
| PAM | Propulsion Avionics Module | In English | → Aeronautics, aircraft |
| PAM | Port Autonome de Marseille (www.marseille-port.fr) | In French | → Transport and postal services |
| PAM | Programme Alimentaire Mondial = PMA | Programa Mundial d'Alimentos | In Asturian = WFP | World Food Programme | In English = WFP | 세계 식량 계획 | In Korean = WFP | მსოფლიო სასურსათო საბჭო | In Georgian = WFP | 国際連合世界食糧計画 | In Japanese = PAM | Programma Alimentare Mondiale | In Italian = PMA | Programa Mundial de Alimentos | In Spanish |
In French | → United Nations → 6123 → Agricultural sciences |
| PAM | Programma Alimentare Mondiale = PMA, WFP (look above) |
In Italian | → United Nations → 6123 → Agricultural sciences |
| PAN | Polyacrylonitrile | In English | → Chemical technology |
| PAN-H | Plan d'Action National sur l'Hydrogène et les piles à combustible | In French | → 6208 |
| PAP | Papanicolaou | In German | → Oncology |
| PAPEETE | Pour Améliorer les Performances Énergétiques ET Environnementales | In French | → Energy economics → Electrical engineering |
| PARAK | Programme d'appui rural Aga Khan | In French | → Development → Agricultural sciences → Regional planning |
| PARE | Physiological and Anatomical Rodent Experiment | In English | → Biological sciences → Zoology → Anatomy |
| PARS | Property Accountability Record System | In English | → Accounting |
| PARS | Property Accounting and Reporting System | In English | → Accounting |
| PAS | Personen uit het Autisme Spectrum | In Dutch | → Neurology |
| PASS | Primary Avionics Software System | In English | → Software → Aeronautics, aircraft |
| PASTISS | Professional Analysis Software Tool for Inflatable Space Structures | In English | → Software → Mechanical engineering |
| PATH | Postflight Attitude and Trajectory History | In English | → Aeronautics, aircraft → Spaceflight engineering, astronautics |
| PATH | Partners for Advanced Transit and Higways | In English | → Organizations and associations → Transport and postal services |
| PATH | Program for Appropriate Technology in Health | In English | → Medicine |
| PATS | Payload Avionics Test Station | In English | → Aeronautics, aircraft |
| PAVC | Pseudomonas Aeruginosa Vaccine Consortium | In English | → Organizations and associations → Immunology and allergy |
| PAW | Plasma Arc Welding | In English | → Plasma physics → Metallurgy |
| PAZE | Podlaska Agencja Zarzidzania Energii | In Polish | → Energy economics |
| PB | Point de Branchement | In French | → Telecommunications |
| PBAN | Polybutadiene Arcylonitrile | In English | → Chemical technology |
| PBB | Polybrominated biphenyl = PBB | Polybromobiphényle | In French = PBB | Polybromierte Biphenyle | In German |
In English | → Chemicals |
| PBB | Polybromobiphényle = (look above) |
In French | → Chemicals |
| PBB | Polybromierte Biphenyle = (look above) |
In German | → Chemicals |
| PBB | Provider Backbone Bridge | In English | → Networks, communication → Telecommunications |
| PBB-TE | Provider Backbone Bridge - Traffic Engineering | In English | → Networks, communication → Telecommunications |
| PBBN | Provider Backbone Bridge Network | In English | → Networks, communication → Telecommunications |
| PBD | Payload Bay Door | In English | → Mechanical engineering |
| PBDAC | Principal Bank for Development and Agricultural Credit | In English | → Banks → Development → Agricultural sciences |
| PBDE | Polybromierte Diphenylether = PBDE | Polybromodiphényléther | In French = PBDE | Polybrominated diphenyl ether | In English |
In German | → Chemicals |
| PBDE | Polybromodiphényléther = (look above) |
In French | → Chemicals |
| PBDE | Polybrominated diphenyl ether = (look above) |
In English | → Chemicals |
| PBDM | Payload Bay Door Mechanism | In English | → Mechanical engineering |
| PBEB | Provider Backbone Edge Bridge | In English | → Networks, communication → Telecommunications |
| PBI | Polybenzimidezole | In English | → Chemical technology |
| PBL | Peripheral Blood Lymphocyte | In English | → Blood and circulatory system → Immunology and allergy |
| PBMC | Peripheral Blood Mononuclear Cell | In English | → Blood and circulatory system |
| PBPS | Postboost Propulsion System | In English | → Vehicle engineering |
| PBR | Ponction-Biopsie Rénale | In French | → Diagnostics |
| PBS | Papier Büro und Schreibwaren | In German | → 676 |
| PBS | Pharmaceutical Benefits Scheme | In English | → Pharmacology, toxicology |