OCR
- Cambridge OCR
- General Services Administration
- OCR-A
- OCR-B
- Obstacle course racing
- Office for Civil Rights
- Office of Justice Programs
- Official cash rate
- Optical character recognition
- Optimum currency region
- Organically moderated and cooled reactor
- Original cast recording
- Otago Central Railway
- Ottawa Central Railway
- OverClocked ReMix
- Oxidizable carbon ratio dating
- Transvaginal oocyte retrieval
- United States Department of Health and Human Services
- United States Department of State