- OPEN LOOK
- open numbering
- open protocol
- open region
- open routine
- open sentence
- open set
- open simplex
- open source
- open subroutine
- open subspace
- open surface
- open system
- open traverse
- open web
- open-ended
- OpenDoc
- opening bracket
- opening price
- opening screen
- opeode map
- operable time
- operand field
- operate
- operate mode
- operating characteristic
- operating console
- operating delay
- operating diskette
- operating environment
- operating instruction
- operating key
- operating maintenance
- operating point
- operating position
- operating potential
- operating ratio
- operating repair
- operating software
- operating space
- operating time
- operation analysis
- operation characteristic
- operation cycle
- operation decoder
- operation expression
- operation field
- operation mode
- operation number
- operation part
- operation priority
- operation progress
- operation register
- operation table
- operation trial
- operation-interface
- operational amplifier
- operational calculus
- operational data
- operational definition
- operational diskette
- operational environment
- operational expression
- operational factor
- operational failure
- operational order
- operational precision
- operational rights
- operational sign
- operative
- operative language
- operator assisted
- operator command
- operator console
- operator endomorphism
- operator hierarchy
- operator interrupt
- operator message
- operator overloading
- operator part
- operator procedure
- operator services
- operator station
- operator theory
- opment system
- opponent
- oppose
- opposing connection
- opposite
- opposite category
- opposite number
- opposite ring
- opposite sense
- oppositely
- oppositely oriented
- opposition
- opposition direction
- optational key
- optical amplifier
- optical character