OAB       One-to-All Broadcast
OAD       Open Architecture Driver [Bernoulli]
OAG       Official Airline Guide , Online Air Guide
OAI       Open Applications Interface
OAS       One-to-All Scatter
OBD       On Board Diagnostics
OBEX      Object Exchange [Borland]
OBJ       Object
OC        Optical Carrier
OCE       Open Collaborative Environment [Apple]
OCF       Objects Components Framework [Borland]
OCL       Operation Control Language , Operator Control Language
OCR       Optical Character Recognition
OCS       On-Card Sequencer
OCX       OLE Custom Control
ODA       Office Document Architecture
ODAPI     Open Database Application Programming
          Interface [Borland]
ODBC      Open Data Base Connectivity [Microsoft]
ODBMS     Object-Oriented Database Management System  (also
          see OODMS)
ODI       Open Datalink Interface [Novell] ,
          Open Device Interconnect [NetWare]
ODM       Object Data Manager [IBM]
ODMA      Open Document Management API
ODP       Open Distributed Processing
ODS       Open Data Services [Microsoft]
ODSI      Open Directory Service Interface [Microsoft]
ODT       Open Desktop
OEM       Original Equipment Manufacturer
OEP       Operand Execution Pipeline
OF        Overflow Flag
OFB       Output Feedback (mode)
OFMT      Output Format for Numbers
OFS       Object File System [Microsoft] , Output Field Separator
OH        Off Hook
OIDL      Object Interface Definition Language
OIS       Office Information Systems
OLAP      On-Line Analytical Processing
.OLD      Old version (file name extension)
OLE       Object Linking and Embedding [Microsoft]
OLI       Optical Line Interface [AT&T]
OLMC      Output Logic Macrocell
OLTP      On-Line Transaction Processing
OM        Object Manager
OMA       Object Management Architecture [Microsoft]
OME       Open Messaging Environment (protocol)
OMF       Object Module Format [Microsoft] ,
          Open Media Framework , Open Message Format
OMG       Object Management Group
OMI       Open Messaging Interface [Lotus]
OMNS      Open Network Management System
OMR       Optical Mark Recognition
ONC       Open Network Computing [Sun]
ONDS      Open Network Distribution Services [IBM]
ONU       Optical Network Unit
OODB      Object-Oriented Database
OODMS     Object-Oriented Database Management System (also
          see ODBMS)
OOL       Object-Oriented Language
OOOS      Object-Oriented Operating System
OOPL      Object-Oriented Programming Language
OOPS      Object Oriented Programming and Systems
OOS       Object-Oriented Systems ,
          Off-line Operating Simulator
OOT       Object-Oriented Technology
OOUI      Object Oriented User Interface
OP        Operation , Optical , Output
OPAC      Online Public Access Catalog [Internet]
OPC       Optical Photoconductor
OPCODE    Operational Code
OPD       Operand
OPI       Open Prepress Interface
OPM       Operations Per Minute
OPS       Operations
OPT       Open Protocol Technology
.OPT      Options (file name extension)
OPUS      Octal Program Updating System
ORACLE    On-Line Inquiry and Report Generator (UNIX DB program)
ORB       Object Request Broker [Microsoft]
ORG       Organization (organization Domain name) [Internet]
ORI       Online Retrieval Interface
.ORI      Original (file name extension)
ORS       Output Record Separator
OS        Operating System
OS/2      Operating System/2 [IBM]
OSA       Open Scripting/System Architecture
OS/E      Operating System/Environment
OSF       Open Software Foundation
OSI       Open Systems Interconnection
OSM       Off-Screen Model
OSP       On-Screen Programming , Optical Storage Processor
OSPF      Open Shortest Path First
OSQL      Object Structured Query Language
OT        Object Technology
OTA       Operation-Triggered Architecture
OTDR      Optical Time Domain Reflectometer
OTF       Open Token Foundation
OTP       One-Time Programmable
OURS      Open Users Recommended Solutions
.OUT      Outlines (file name extension)
OUTS      Output String
OV        Overflow
.OVL      Program Overlay (file name extension)
.OVR      Program Overlay (file name extension)
OWL       Object/Open Windows Library [Borland]