List of acronyms and initialisms: O

This list contains acronyms, initialisms, and pseudo-blends that begin with the letter O.

For the purposes of this list:

• acronym = an abbreviation pronounced as a series of constituent letters, e.g., SARS = severe acute respiratory syndrome
• initialism = an abbreviation pronounced wholly or partly using the names of its constituent letters, e.g., CD = compact disc
• pseudo-blend = an abbreviation whose extra or omitted letters means that it cannot stand as a true acronym, initialism, or portmanteau (a word formed by combining two or more words).

(a) = acronym in the example: SARS – (a) Severe acute respiratory syndrome

(i) = initialism in the example: CD – (i) Compact disc

(p) = pseudo-blend in the example: UNIFEM – (p) United Nations Development Fund for Women

(s) = symbol (none of the above, representing and pronounced as something else; for example: MHz – Megahertz)

(Main list of acronyms and initialisms)

• O – (i) Oberst – Observer – Obstacle – Octal – Officer – Official – Oh – Operational – Operator – Oprah (magazine) – Outstanding – (s) Oxygen

OA

• OA – (i) Operational Analysis – (i) Overeaters Anonymous
• OAC – (i) On Approved Credit
• OAP – Old Age Pensioner (UK)
• OAS – (i) Organization of American States
• OARSI – (i) Osteoarthritis Research Society International
• OASIS – (a) Objects and Agents for Information Systems and Simulation – Organization for the Advancement of Structured Information Standards
• OASIS – (a) Ontario Agencies Supporting Individuals with Special Needs
• OASIS – (a) Ontario Association of Sewage Industry Services
• OASP – (i) Operational Analysis Support Paper/Plan
• OAU – (i) Organization for African Unity

OB

• ob – (p) obiit (Latin, "(s) he died")
• OB – (p) Obedience – Obligation – Obligatory – Obsolete – Obstetrics – (i) Ocean Beach (California) – Off Break (cricket) – Old Bryanstonian – Order of Battle – Outlet Box (electrical) – (p) Overbought (stock market) – (i) Oversight Board
• OBE – (i) Officer of the Order of the British Empire
• OBJ – (p) Objective (military parlance)
• OBS – (p) Observation/Observer – Obsolete – Obstacle – (i) Off Balance Sheet – Optical Burst Switching (IEEE) – Organic Brain Syndrome – Organization(al) Breakdown Structure
• OBSS – (i) Off Board Sensor Systems – Ordo Byantinus Sancti Sepulchri (Byzantine Order of the Holy Sepulchre) – Orbiter Boom Sensor System (space shuttle) – Origins Billion Star Survey
• OBX – (p) Outer Banks (North Carolina)

OC

• oc – (s) Occitan language (ISO 639-1 code)
• OC – (i) Officer Commanding
• OCA – (i) Observatoire de la Côte d'Azur – Offensive Counter-Air
• OCD – (i) Obsessive-Compulsive Disorder
• OCFS – (i) Oracle Cluster File System
• OCFS [1] – (i) Office of Children & Family Services
• OCFS2 – (i) Oracle Cluster File System Release 2
• oci – (s) Occitan language (ISO 639-2 code)
• OCIDS – (i) Optical Combat Identification System
• OCMCC – (i) [2] Orchard County MCC
• OCN – (i) Oncology Certified Nurse
• OCO – (i) Oort Cloud Object
• OCOKA – (a) Observation, Cover and concealment, Obstacles, Key terrain, and Avenues of approach (mnemonic)
• OCR – (i) Optical Character Recognition
• OCS – see entry

OD

• OD
  • (i) Old Dragon
  • Ordnance Datum (nautical charts)
  • (p) Overdose
• ODAS – (a) OCA-DLR Asteroid Survey
• ODB
  • (i) Ol' Dirty Bastard (rapper)
  • (i) One Dirty B*tch (professional wrestler)
  • (i) Operational Data Base
  • (i) Oxford Dictionary of Byzantium
• ODBC – (i) Open DataBase Connectivity
• ODI
  • (i) Office for Disability Issues (UK government agency)
  • One Day International (cricket)
  • Open Data-Link Interface
  • Oracle Data Integrator
  • Overseas Development Institute (UK think tank)

OE

• OEA – (i) (U.S.) Office of Economic Adjustment
• OED – (i) Oxford English Dictionary
• OECD – (i) Organisation for Economic Co-operation and Development (international)
• OEG – (i) Operation Exposure Guidance
• OEIS - (i) On-Line Encyclopedia of Integer Sequences
• OEM – (i) Original Equipment Manufacturer

OF

• OFA – (i) Occipital Face Area
• OFDA – (i) U.S Agency for International Development's Office of Foreign Disaster Assistance

OG

• OG:
  • Objective Glass, see Objective (optics)
  • Obstetrics and gynaecology
  • Offensive Guard, see Guard (American football)
  • Old Giggleswickian, a former pupil of Giggleswick School
  • Old Gower, a former pupil of University College School
  • Old Gregorian, a former pupil of Downside School
  • Old Greshamian, a former pupil of Gresham's School
  • Old Gold, a dark yellow
  • Olympic Games
  • Original Gangster, see Gangster
  • Original Gravity, see Gravity (beer)
  • Outpost Gallifrey, a Doctor Who fansite.
  • Own goal, in soccer, a goal scored by a player in their own side's goal
  • OG: Optimized Gaia, theory the earth optimizes itself to promote life, and popular movement to Promote Human Progress in Harmony with the Natural World.
  • OG: Original Gangster, an album by Ice-T
• OGC – (i) Open Geospatial Consortium
• OGD – (i) Other Government Department
• OGO – (i) Other Government Organization
• OGX – OUARGLA – a petroleum state in the south of Algeria

OH

• OH – (s) Ohio (postal symbol)
• OHC – (i) OverHead-Cam engine
• OHHLA – (a) Original Hip-Hop Lyrics Archive
• OHIP – (a) Ontario Health Insurance Plan
• OHP – (i) Observatoire de Haute-Provence
• OHSS – (p) Ovarian Hyperstimulation Syndrome

OI

• OIC – (i) Officer In Charge
• OIE – (i) World Organisation for Animal Health (originally the Office international des épizooties, French for "International Epizootic Office")
• OIF – (i) Operation Iraqi Freedom
• OIOC – (i) Oriental & India Office Collections (in the British Library)

OJ

• oj – (s) Anishinaabe language (Ojibwa) (ISO 639-1 code)
• OJ – (i) Orange Juice – O.J. Simpson
• oji – (s) Anishinaabe language (Ojibwa) (ISO 639-2 code)
• OJT – On-the-Job Training

OK

• OK – (s) Oklahoma (postal symbol) – (i) oll korrect (facetious alteration of "all correct", 1839)
• OKC – (a) Oklahoma City

OL

• OLED – (a) Organic Light-Emitting Diode
• OLS – (i) Operational Linescan System

OM

• om – (s) Oromo language (ISO 639-1 code)
• OM – (s) Oman (ISO 3166 digram) – Olympique de Marseille (French football club)
• OMA – (i) Open Mobile Alliance – Operations & Maintenance, Army
• OMB – (i) U.S. Office of Management and Budget – Ontario Municipal Board – (i) Order of Mapungubwe in Bronze
• OMD – (i) Orchestral Manoeuvres in the Dark (1980s pop group)
• OME – (i) Osaka Mercantile Exchange
• OMFG – (i) Oh My Fucking God
• OMG – (i) Oh My God or Or My Gosh
• OMGW – (i) "Oh My Gosh it's Windy"
• OMN – (s) Oman (ISO 3166 trigram)
• OMNCS – (i) U.S. Office of the Manager for the National Communications System
• OMP – (i) Order of Mapungubwe in Platinum
• OMR – (s) Omani rial (ISO 4217 currency code)
• OMS – (i) Order of Mapungubwe in Silver
• OMT – (i) Object Model Template
• OMW – (i) On My Way, Oh My Word

ON

• ON – (s) Ontario (postal symbol)
• Onna – Oniong, Nnung Ndem, and Awa, a Local Government Area in Nigeria
• ONC – (i) Orthopaedic Nurse Certified
• ONCE – (a) Organización Nacional de Ciegos Españoles (Spanish, "National Organization for the Spanish Blind")
• ONÉRA – (a) Office national d'études et de recherches aérospatiales (French, "Aeronautics and Space Research Center")
• ONG – (i) Orthodontic National Group
• ONH – (i) Óglaigh na hÉireann (Irish idiom for "soldiers of Ireland"), used for the following:
  • Historically, as the Irish-language name for the original Irish Republican Army ("Old IRA")
  • In modern times, as the Irish-language name of the Defence Forces of Ireland
  • The name of two groups claiming descent from the Old IRA, one a currently inactive splinter group of the Continuity IRA and the other an active splinter group of the Real IRA
• ONI – (i) (U.S.) Office of Naval Intelligence
• ONS – (i) Operational Needs Statement

OO

• OO – (i) Object Oriented – Over & Out
• OOO – (i) Out Of the Office
• OOAD – (i) Object Oriented Analysis and Design
• OOBE – (a) Out-of-body experience
• OOCL – (i) Orient Overseas Container Line
• OODA – (i) Observation, Orientation, Decision, Action loop (a.k.a. Boyd's Loop)
• OOP – (i) Object-Oriented Programming – Out Of Print
• OOS – (i) Occupational Overuse Syndrome – OneSAF Objective System – Open Operating System – Out Of Service
• OOTW – (i) Operations Other Than War

OP

• OP
  • (i) Observation Point/Post
  • Ocean Pacific (surfwear and swimwear brand)
  • Original Poster (internet)
  • Order Point, in inventory management; the inventory state at which more items should be ordered. Often expressed as a part of OP/OQ (when quantity OP is reached, order OQ new items)
• OPA – (i) Other Procurement, Army
• OPAC – (a) Online Public Access Catalogue
• op cit – (p) opera citata (Latin, "in the work cited")
• OPCON – (p) Operational control
• OPCW – (i) Organisation for the Prohibition of Chemical Weapons
• OPEC – (a) Organization of Petroleum Exporting Countries
• OPFOR – (p) Opposing force(s)
• OPI
  • (i) Office of Primary Interest
  • Open Prepress Interface
• OPINTEL – (p) Operational Intelligence
• OPLAN – (p) Operation plan (also OpPlan)
• OPORD – (p) Operation order
• OPP
  • (i) Ontario Provincial Police
  • Operational Planning Process
  • Other People's Property/Pu**y/Penis (song)
• OPS
  • (i) On-base plus slugging (baseball statistics)
  • (p) Operations
• OPSEC
  • (p) Operations security
  • Open Platform for Security
• OPSI
  • (a) Overwhelming post splenectomy infection
  • UK Office of Public Sector Information
• OPTAR – (p) Operational target
• OPV – (i) Offshore Patrol Vessel

OQ

• OQ
  • Order Quantity, in inventory management; the quantity of new items to be ordered. Often expressed as a part of OP/OQ (when quantity OP is reached, order OQ new items)

OR

• or – (s) Oriya language (ISO 639-1 code)
• OR – (i) Operating Room (surgery) – Operational/Operations Research – (s) Oregon (postal symbol)
• ORAU – (a/i) Oak Ridge Associated Universities
• ORB – (a/i) Object Request Broker
• ORBAT – (p) Order of Battle
• ORD – (i) O'Hare International Airport in Chicago, Illinois (IATA Airport Code ORD)
• ORD – (i) Office of Research and Development – Operational Requirements Document
• ORF – (i) Operational Readiness Float
• ori – (s) Oriya language (ISO 639-2 code)
• ORISE – (a) Oak Ridge Institute for Science and Education
• orm – (s) Oromo language (ISO 639-2 code)
• ORNL – (i) Oak Ridge National Laboratory
• ORR – (i) Oak Ridge Reservation (U.S. DOE) – Office of Rail Regulation (UK government) – Office of Refugee Resettlement – (CIA) Office of Research and Reports – Operational Readiness Rate – Operational Readiness Review
• ORSA – Oxacillin-resistant Staphylococcus aureus – Operations Research Society of America

OS

• OS – (s) Operating System
• os – (s) Ossetic language (ISO 639-1 code)
• Os – (s) Osmium
• OSA – (i) Order of St. Augustine
• OSCE – (i) Organisation for Security and Cooperation in Europe
• OSD – (i) U.S. Office of the Secretary of Defense – (i) On-screen Display
• OSDL – (i) Open Source Development Labs
• OSE – (a) Own Separate Entrance
• OSERS – (a) U.S. Department of Education Office of Special Education and Rehabilitative Services
• OSETI – (a) Optical SETI also Optical SETI
• OSHA – (a) Occupational Safety and Health Administration
• OSI – (i) Office of Strategic Influence – Ontario Swine Improvement – Open Source Initiative – Open Systems Interconnection
• OSIA – (i) (U.S.) On-Site Inspection Agency
• OSL – (i) Open Source License – Optically Stimulated Luminescence – Orbiting Solar Laboratory
• OSM – (i) One Saturday Morning
• OSOTPBOIAS – (i) One Sec, On The Phone, Be Off In A Sec
• OSPA – (a) Operations Security Professional's Association site of OSPA
• OSPA – (i) Oregon School Psychologists Association [3]
• OSRH – (i) Oružane Snage Republike Hrvatske (en: Armed forces of the Republic of Croatia)
• oss – (s) Ossetic language (ISO 639-2 code)
• OSS – (i) Office of Strategic Services (1942–1945, forerunner of CIA)
• OSU – (i) Ohio State University – Oklahoma State University

OT

• OTA – (i) Office of Technology Assessment – (a/i) Orthodontic Technicians Association
• OTAC – (i) Orthodontic Technicians Association Conference – (i) Orthodontic Technicians Association Council
• OTB – (i) Off The Ball – (i) Offtrack Betting – (p) OneSAF Testbed (a descendant of ModSAF)
• OTC – (i) Over-The-Counter (drugs)
• OTEA – (i) (U.S. Army) Operational Test Evaluation Agency
• OTI – (i) Office of Transition Initiatives (United States Agency for International Development)
• OTO – (i) Ordo Templi Orientis (Latin, "Order of the Temple of the East", i.e. the Order of Oriental Templars)
• OTOH – (i) On The Other Hand
• OTSBH – (i) Over The Shoulder Boulder Holder
• OTW – (i) On The Way
• OTYBL – (i) Over To You Blue Leader

OU

• OU – (p) University of Oklahoma

OV

• OVC – (s) Overcast (METAR Code) – (i) Ohio Valley Conference
• OVV – (i) Optically Visually Violent, or Optically Violently Variable – a type of quasar

OW

• OW – (i) Old Wykehamist
• OWN – (i) Oprah Winfrey Network

OZ

• OZ – (?) Australia