| O | Oxygen |
| O | Oh |
| o | octet |
| O | Oberst |
| O | Pyrrolysine |
| O/o | Office of |
| O2 | Oxygen |
| O2O | Online to Offline |
| O3b | Other 3 billion |
| OAB | Oman Arab Bank |
| OAS | Oracle Application Server |
| OAS | Option Adjusted Spread |
| OAS | Office of Applied Studies |
| OAS | Organization of American States |
| OAuth | Open Authorization |
| OBC | Oriental Bank of Commerce |
| OBC | Organic & Biomolecular Chemistry |
| OBC | Orquestra Simfònica de Barcelona i Nacional de Catalunya |
| OBC | Other Backward Class |
| OBC | Order of British Columbia |
| OBC | Osaka Broadcasting Corporation |
| OBC | Osservatorio Balcani e Caucaso |
| OBC | Ontario Building Code |
| OBC | Over Betuwe College |
| OBD | On-Board Diagnostics |
| OBD | Outbound Dialler |
| OBD | Opposed Blade Damper |
| OBD | Obano Airport |
| OBD | Organic Brain Disease |
| OC | Original Content |
| OC | Orange County |
| OC | Open Circuit |
| OC | OverClocking/OverClock |
| OC | Original Character |
| OC | Ocean City |
| oc | Occitan |
| OC | Organic Carbon |
| OC | Optical Carrier |
| OC | Oral Contraceptive |
| OC | Oberlin College |
| OC | Open Collector |
| OC | Octopus Card |
| OC | Oleoresin Capsicum |
| OCBC | Oversea-Chinese Banking Corporation |
| OCBC | Orange County Business Council |
| OCBC | Orange County Buddhist Church |
| OCBC | Old Cambridge Baptist Church |
| OCBC | Oakland Cannabis Buyers’ Cooperative |
| OCBC | Orange County Badminton Club |
| OCD | Obsessive Compulsive Disorder |
| OCD | Osteochondritis Dissecans |
| OCD | Office of Civilian Defense |
| OCI | Other Comprehensive Income |
| OCI | Oracle Cloud Infrastructure |
| OCI | Oracle Call Interface |
| OCI | Overseas Citizenship of India |
| OCI | Orascom Construction Industries |
| OCI | Organisation de la Coopération Islamique |
| OCI | On-Campus Interview |
| OCI | Office of Criminal Investigations |
| OCI | Open Catalog Interface |
| OCI | Open Container Initiative |
| oci | Occitan |
| OCI | Organizational Conflict of Interest |
| OCI | Olympic Council of Ireland |
| OCI | Ontario Cancer Institute |
| OCI | Organisation Communiste Internationaliste |
| OCI | Oakwood Collegiate Institute |
| OCI | Open Constitution Initiative |
| OCP | Oracle Certified Professional |
| OCR | Optical Character Recognition |
| OCR | Office for Civil Rights |
| OCR | Office for Civil Rights |
| OCR | Oxford, Cambridge and RSA Examinations |
| OCR | Official Cash Rate |
| OCR | Official Cash Rate |
| OCR | Optimal Currency Region |
| OCR | Old Cask Rum |
| Oct | October |
| OCT | Office of Cable Television |
| Oct | Octal |
| OCT | Optical Coherence Tomography |
| OCT | Oxford Classical Texts |
| OCT | Ontario College of Teachers |
| OCT | Oxytocin Challenge Test |
| OCT | Optimal Control Theory |
| OCV | Open Circuit Voltage |
| OD | Doctor of Optometry |
| OD | Overdraft |
| OD | Malindo Air |
| OD | Optical Density |
| OD | Organization Development |
| OD | Occupational Disease |
| OD | Outside Diameter |
| OD | Overdose |
| OD | Opportunistic Disease |
| OD | Oxygen Demand |
| ODA | Official Development Assistance |
| ODA | Open Document Architecture |
| ODA | Oregon Department of Agriculture |
| ODA | Olympic Delivery Authority |
| ODA | Ohio Dental Association |
| ODA | Ouadda Airport |
| ODBC | Open Data Base Connectivity |
| ODFL | Old Dominion Freight Line |
| ODFL | Open, Distance and Flexible Learning |
| ODFL | One Dollar For Life |
| ODFL | Omeo and District Football League |
| ODI | One Day International |
| ODI | Overseas Development Institute |
| ODP | Open Directory Project |
| ODP | Ocean Drilling Program |
| OE | Outlook Express |
| OECD | Organisation for Economic Co-operation and Development |
| OECD | Office for Early Childhood Development |
| OED | Oxford English Dictionary |
| OED | Oregon Employment Department |
| OEM | Original Equipment Manufacturer |
| OEM | Office of Emergency Management |
| OEM | Oracle Enterprise Manager |
| OEM | Object Exchange Model |
| OEM | Vincent Fayks Airport |
| OFB | Output FeedBack |
| OFB | Ordnance Factories Board |
| OFB | Open for Business |
| OFC | Optical Fiber Communication |
| OFC | Orbitofrontal Cortex |
| OFC | Oxygen Free Copper |
| OFC | Optical Fiber Cable |
| ofc | of course |
| OFC | Oceania Football Confederation |
| OFC | Corporate Office Properties Trust |
| OFC | Offshore Financial Centre |
| OFC | Open Face Chinese |
| OFC | Oxyfuel Gas Cutting |
| OFC | Optional Federal Charter |
| OFC | Oxford Farming Conference |
| OFC | Open Fiber Control |
| OFC | Open Financial Connectivity |
| OFC | Original Fine Canadian |
| OFC | Ottawa Folklore Centre |
| OFC | Optical Fiber Conductive |
| Ofgem | Office of Gas and Electricity Markets |
| Ofgem | Office of Gas and Electricity Markets |
| Ogg | Ogg derives from ogging, jargon from the computer game Netrek |
| OGG | Kahului Airport |
| OGPA | Overall Grade Point Average |
| OHCHR | Office of the United Nations High Commissioner for Human Rights |
| Ohm | named after German physicist, Georg Simon Ohm |
| OHP | OverHead Projector |
| OHP | Oregon Health Plan |
| OHP | Observatoire de Haute-Provence |
| OHP | Occupational Health Psychology |
| OHP | Oklahoma Highway Patrol |
| OHP | Open House Party |
| OHP | Open Humanities Press |
| OHP | Order of The Holy Paraclete |
| OHV | Off Highway Vehicle |
| OHV | OverHead Valve |
| OIDAR | Online Information and Database Access or Retrieval |
| OIGS | Osaka International Gift Show |
| OIGS | Outreach Institute of Gender Studies |
| OIL | Oil India Limited |
| OIL | Operation Iraqi Liberation |
| OIL | Ontology Inference Layer |
| OK | Oll Korrect |
| OK | Oklahoma |
| OK | Old Kinderhook |
| OK | Czech Airlines |
| OLED | Organic Light-Emitting Diode |
| OLEDB | Object Linking and Embedding, Database |
| OLX | On Line eXchange |
| OMAP | Open Multimedia Application Platform |
| OMC | Organización Mundial del Comercio |
| OMC | Organisation Mondiale du Commerce |
| OMC | Organização Mundial do Comércio |
| OMC | Omnicom Group Inc. |
| OMC | Open Method of Coordination |
| OMC | Odisha Mining Corporation |
| OMC | Oil Marketing Company |
| OMC | Ormoc Airport |
| OMC | Operation and Maintenance Center |
| OMC | Octyl-methoxycinnamate |
| OMC | Ordem do Mérito Cultural |
| OMC | Outboard Marine Corporation |
| OMC | Olifant Manufacturing Company |
| OMC | Oxford Mindfulness Centre |
| OMC | Osaka Medical College |
| OMC | Otara Millionaires Club |
| OMC | Ontario Medal for Good Citizenship |
| OMFED | Orissa State Cooperative Milk Producers’ Federation Limited |
| OMG | Oh My God |
| OMG | Object Management Group |
| OMG | Ocular Myasthenia Gravis |
| OMR | Omani Rial |
| OMR | Old Mahabalipuram Road |
| OMR | Optical Mark Recognition |
| OMR | Optical Mark Reader |
| OMR | Oradea Airport |
| OMR | Optical Music Recognition |
| OMR | Outermost Regions |
| OMR | Ontario Medical Review |
| OMS | Organisation Mondiale de la Santé |
| OMS | Order Management System |
| OMW | On My Way |
| OMW | Ogden Murphy Wallace |
| ONGC | Oil and Natural Gas Corporation |
| Onkyo | translates as “sound harmony” |
| ONVIF | Open Network Video Interface Forum |
| OODBMS | Object-Oriented Data Base Management System |
| OOO | Out of Order |
| OOo | OpenOffice.org |
| OOO | Out of Office |
| Ooo | Alturas Municipal Airport |
| OOP | Object-Oriented Programming |
| OOPS | Out Of Phase Stereo |
| OOPS | Out of Paper Sensor |
| OOTD | Outfit Of The Day |
| OOTD | Offer of the Day |
| OOTN | Outfit Of The Night |
| OOTW | Operations Other Than War |
| OOTW | Outfit(s) Of The Week |
| OP | Original Post/Poster |
| OP | One Piece |
| OP | Ocean Pacific |
| OP | OutPatient |
| OP | Optimus Prime |
| Op | Opus number |
| OP | Ordo Praedicatorum |
| OP | OverPowered |
| OP | Observation Post |
| OP | OrganoPhosphate |
| OP | Out of Print |
| OP | Original Pronunciation |
| OP | Operational Planning |
| OP | OsuusPankki |
| OP | Orange Pekoe |
| OP | Overall Position |
| OP | Overland Park |
| OP | Opposite Prompt |
| Op | Order in probability |
| OP | Oratory Prep |
| op | oborový podnik |
| OPAC | Online Public Access Catalog |
| OPAC | Office Proficiency Assessment and Certification |
| OPC | OLE for Process Control |
| OPC | One Person Company |
| OPC | Optical Proximity Correction |
| OPC | Optimum Power Calibration |
| OPC | Orthodox Presbyterian Church |
| OPC | Office of the Parliamentary Counsel |
| OPC | Organic Photo-Conductor |
| OPC | Opel Performance Center |
| OPC | Ontario Police College |
| OPC | Otsuka Pharmaceutical Company |
| OPC | Oligomeric Proanthocyanidins |
| OPC | Oodua Peoples Congress |
| OPC | Ovamboland People’s Congress |
| OPD | Oakland Police Department |
| OPD | Outpatient Department |
| OPD | Orlando Police Department |
| OPEC | Organization of Petroleum Exporting Countries |
| OPEC | Ohio Prevention and Education Conference |
| OPeNDAP | Open-source Project for a Network Data Access Protocol |
| OPGW | Optical Ground Wire |
| OPORD | Operation(s) Order |
| Opp | Opposite |
| OPP | Ontario Provincial Police |
| OPP | Object Push Profile |
| OPP | Over Power Protection |
| OPP | Ovine Progressive Pneumonia |
| OPP | Office of Pesticide Programs |
| OPP | Orangi Pilot Project |
| OPP | Ortho-Phenylphenol |
| OPP | Office of Polar Programs |
| OPP | Office of Public Prosecutions |
| OPP | Offentligt-Privat Partnerskab |
| OPP | Office of Physical Plant |
| OPP | Orleans Parish Prison |
| OPP | Open Prosthetics Project |
| OPR | Operator/Operate/Operation |
| OPR | Office of Population Research |
| OPR | Office of Professional Responsibility |
| OPR | Overall Pressure Ratio |
| OPR | Overnight Policy Rate |
| OPR | Organisation du Peuple Rodriguais |
| OPR | Old Parochial Registers |
| OPR | Old Port Rum |
| OPS | Office of Public Safety |
| OPS | Omaha Public Schools |
| OPS | Oracle Parallel Server |
| OPS | Ottakara Panneerselvam |
| OPS | Optical Parking System |
| OPS | Ottawa Police Service |
| OPS | On-Base Plus Slugging |
| OPSM | Optical Prescription Spectacle Makers |
| OPSM | Oracle Parallel Server Management |
| OR | Oregon |
| or | Oriya |
| OR | Odds Ratio |
| OR | ArkeFly |
| Oracle | the name Oracle comes from the code name of a CIA project |
| Oral-B | Oral-Brush |
| OrCAD | Oregon + CAD |
| org | Organization |
| ORG | Oxford Research Group |
| ORG | Open Rights Group |
| ORG | Zorg en Hoop Airport |
| Orkut | named after its creator, Orkut Büyükkökten |
| ORM | Object-Relational Mapping |
| ORM | Operational Risk Management |
| ORM | Online Reputation Management |
| ORM | Object-Role Modeling |
| ORM | Sywell Aerodrome Airport |
| orm | Oromo |
| ORM | Orion Metals Limited |
| ORM | Observatorio del Roque de los Muchachos |
| ORM | Orosomucoid |
| ORS | Oral Rehydration Solution |
| ORS | Olfactory Reference Syndrome |
| ORS | Orthopaedic Research Society |
| ORS | Old Red Sandstone |
| ORS | Oregon Revised Statutes |
| ORS | Overseas Research Scholarship |
| ORS | Oxygen Reduction System |
| ORS | Oculo-Respiratory Syndrome |
| ORS | OID Resolution System |
| ORS | Orcas Island Airport |
| ORVM | Outside Rear View Mirror |
| OS | Operating System |
| OS | Open Source |
| OSCE | Organization for Security and Co-operation in Europe |
| OSCE | Objective Structured Clinical Examination |
| OSCON | O’Reilly Open Source Convention |
| OSD | On-Screen Display |
| OSHA | Occupational Safety and Health Administration |
| OSHA | Occupational Safety and Health Association |
| OSHA | Oregon Speech-Language-Hearing Association |
| OSI | Open Systems Interconnection |
| Osram | Osmium + Wolfram |
| OSRTC | Odisha State Road Transport Corporation |
| OSS | Open Source Software |
| OSS | Open Sound System |
| OSS | Office of Strategic Services |
| OSV | Our Sunday Visitor |
| OSV | Original Seen & Verified |
| OSV | Offshore Supply Vessel |
| OSV | Old Sturbridge Village |
| OT | Occupational Therapist |
| OT | Occupational Therapy |
| OT | Operation Theatre |
| OT | Operational Technology |
| OT | Off-Topic |
| OT | Oxytocin |
| OT | OverTime |
| OT | Operación Triunfo |
| OT | Obrněný Transportér |
| OT | Old Testament |
| OT | Optimality Theory |
| OT | OverTime |
| OT | Operation Transformation |
| OT | Organisation Todt |
| OT | Oyu Tolgoi |
| OT | Operating Thetan |
| OT | Oblivious Transfer |
| OT | Operational Transformation |
| OT | Offensive Tackle |
| OT | Aeropelican Air Services |
| OTA | Over-the-air |
| OTA | Office of Technology Assessment |
| OTA | Organic Trade Association |
| OTA | Orthodontic Technicians Association |
| OTA | Operational Transconductance Amplifier |
| OTC | Over The Counter |
| OTC | OpenText Corporation |
| OTC | Over The Counter |
| OTC | Osaka Titanium Technologies |
| OTC | Ozarks Technical Community College |
| OTC | Ornithine Transcarbamylase |
| OTCEI | Over the Counter Exchange of India |
| OTE | On-Target Earnings |
| OTE | Οργανισμός Τηλεπικοινωνιών Ελλάδος |
| OTE | Oxygen Transfer Efficiency |
| OTE | Optically Transparent Electrode |
| OTET | Ovarian-Type Epithelial Tumors |
| OTET | Orissa Teachers Eligibility Test |
| OTG | On-The-Go |
| OTG | Over The Glasses |
| OTG | Oven Toaster Griller |
| OTG | Off-The-Grid |
| OTG | Worthington Airport |
| OTG | Octyl Thioglucoside |
| OTG | One Two Go Airlines |
| OTM | One Time Mandate |
| OTM | Ottumwa |
| OTM | OSHA Technical Manual |
| OTM | Open Tip Match |
| OTM | Ottumwa Regional Airport |
| OTM | Of The Month |
| OTM | Office of Technology Management |
| OTM | On the Media |
| OTM | Operations and Technology Management |
| OTM | On the Move |
| OTP | One Time Password |
| OTP | One Time Programmable |
| OTP | Opposite Track Path |
| OTP | Bucharest Otopeni International Airport |
| OTP | Out of Turn Priority |
| OTT | Over-The-Top |
| OTT | Ottawa |
| OTT | OpenDocument Text Template |
| OTT | Overseas Trained Teacher |
| OTT | One-Time Tape |
| OU | Open Universities |
| OU | Open University |
| OU | University of Oklahoma |
| OU | Ohio University |
| OU | Osmania University |
| OUP | Oxford University Press |
| OUP | Ornstein–Uhlenbeck Process |
| OVRM | Overdimension Vehicle Route Maps |
| OVRM | Okanagan Vacation Rental Management |
| OWASP | Open Web Application Security Project |
| Oxfam | Oxford Committee for Famine Relief |
| Oy | Osakeyhtiö |
| OYEC | Own Your Electric Connection |
| Oyj | Julkinen Osakeyhtiö |
| OYO | On Your Own |
| OYO | Ombetja Yehinga Organisation |
| oz | Ounce |
| OZ | Asiana Airlines Inc. |
| OZ | Olimpia Zagnoli |
| Ozone | named after the Greek verb Ozein (to smell), from the peculiar odor in lightning storms |
