OA Office Automation
OA Overeaters Anonymous
OAO Orbiting Astronomical Observatory (Espacial)
OAS Organization of American States
OATS Office Automation Technology and Services
OBE Order of the British Empire
OBS Omni Bearing Selector
OC Order of Canada
OCDM Office of Civil Defense and Mobilization
OCI Out of City Indicator
OCLC Online Computer Library Center, Inc.
OCLC Online Computer Library Center (Ohio College Library Catalog)
OCO Object Code Only
OCR Optical Character Recognition
OCS Officer Candidate School
OCST Office of Commercial Space Transportation (Espacial)
OD Doctor of Optometry
OD Oculus Dexter (olho certo)
OD Officer of the Day
OD OverDose
ODI Optical Digital Image
ODISS Optical Digital Image Storage System
ODT Octal Debugging Technique
ODT Online Debugging Technique
OE Old English
OED Oxford English Dictionary
OEM Original Equipment Manufacturer
OEO Office of Economic Opportunity
OES Order of the Eastern Star
OEXP Office of Exploration [NASA]
OF Old French
OFM Order of Friars Minor
OFS Order of Free State
OG Original Gum
OH Ohio
OIRA Office of Information and Regulatory Affairs
OIU Office Interface Unit
OJT On the Job Training
OLTP On-Line Transaction Processing
OMB Office of Management and Budget (Governo americano)
OMD Orchestral Manouevers in the Dark
OMS Orbital Maneuvering System (Espacial)
OMV Orbital Maneuvering Vehicle (Espacial)
ON Old Norse
ONC Open Network Computing
ONI Office of Naval Intelligence
ONI Operator Number Identification (Telefonia)
ONR Office of Naval Research
OOP Object Oriented Programming
OOPART Out Of Place ARTifact
OOPS Object-Oriented Programming System
OP Observation Post
OP OFFICEPOWER office automation system, trademark of CCI
OP Order of Preachers
OP Out of Print
OPEC Organization of Petroleum Exporting Countries
OPF Orbiter Processing Facility (Espacial)
OPM Office of Personnel Management
OPUS Obvious Password Utility System (Eugene Spafford <Spaf@Purdue.Edu>)
OR Operating Room
OR Oregon
OR Owner's Risk, Own Risk
ORFEUS Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer (Espacial)
ORNL Oak Ridge National Laboratory
OROM Optical Read Only Memory
OS Oculus Sinister (left eye)
OS Operating System
OS Ordinary Seaman
OS Out of Stock
OSB Order of St. Benedict
OSC Orbital Sciences Corporation (Espacial)
OSCAR Orbiting Satelite Carry Amateur Radio (1º lançado em 12 Dez 1961)
OSCAR Orbiting Satellite Carry Amateur Radio (1º lançado em 12 Dez 1961)
OSCAR Orbiting Satellite Carrying Amateur Radio (Espacial)
OSCRL Operating System Command Response Language
OSD Office of the Secretary of Defense
OSDIT Office of Software Development and Information Technology
OSF Open Software Foundation
OSF Open Systems Foundation
OSF Order of St. Francis
OSHA Occupational Safety and Health Administration (Governo americano)
OSI Office of Scientific Integrity [NIH]
OSI Open Systems Interconnection (por ISO; 7 modelos)
OSI/RM Open Systems Interconnection/Reference Model
OSME Open Systems Message Exchange
OSP Optical Storage Processor
OSPFIGP Open Shortest-Path First Internal Gateway Protocol [Internet]
OSS Office of Strategic Services (depois CIA)
OSS Office Support System
OSS Operation Support System [Telefonia, AT&T]
OSSA Office of Space Science and Applications (Espacial)
OSSE Oriented Scintillation Spectrometer Experiment (em GRO) (Espacial)
OSTP Office of Science and Technology Policy
OSTP (Casa Branca) Office of Science and Technology Policy (Governo americano)
OT Old Testament
OT OverTime
OTA Office of Technical Assistance
OTA Office of Technology Assessment
OTA Optical Telescope Assembly (em HST) (Espacial)
OTB Off-Track Betting
OTC Over The Counter 
OTF Open Token Foundation
OTH-B Over The Horizon - Backscatter (como em radar)
OT&LF Open Taxi & Limousine Foundation
OTR On The Rag
OTS Officers' Training School
OTV Orbital Transfer Vehicle (Espacial)
OUTWATS OUTward Wide Area Telephone Service (Telefonia)
OV Orbital Vehicle (Espacial)
OV Orbiter Vehicle (Espacial)
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