O
- occupational
- occupational safety
- occupied bandwidth
- occurrence
- occurrence of event
- OCD
- OCF
- OCh
- OCI
- OCIL
- OCIP
- OCIS
- OCO
- OCP
- OCP-IP
- OCR
- OCR-A font
- OCS
- OCSP
- octahedron
- octal
- octal constant
- octal integer
- octal notation
- octal number
- octal number
- octal numeral
- octal numeration system
- octal representation
- octet
- octocopter
- octonary
- octothorp
- octree
- OCU
- OCV
- OCX
- OCXO
- OD
- ODA
- ODAPI
- ODBC
- ODbL
- odd
- ODD
- odd parity
- odd vertex
- odd-even check
- ODF
- ODI
