OP
- 0P (disambiguation)
- Anime OP
- Glossary of tennis terms
- List of Old Paulines
- O'Brien Peak
- O'Cain Point
- O'Connor Peak
- O'Donnell Peak
- O'Fallon Park
- O'Higgins Park
- O'Leary Peak
- O'Neal Point
- O'Neill Peak
- O'Neill Point
- O'Neill Regional Park
- O'Shea Peak
- O'Sullivan Peak
- O.P. Anderson
- OP Financial Group
- OPS (disambiguation)
- Oborový podnik
- Observation post
- Ocean Pacific
- Octagonal prism
- Odisha Police
- One Piece
- Op (statistics)
- Op-ed
- Op. cit.
- Open Philanthropy
- Operation (disambiguation)
- Operational planning
- Operator (disambiguation)
- Ops (disambiguation)
- Optimus Prime
- Orange Pekoe
- Oratory Preparatory School
- Orchard Park, New York
- Order of Preachers
- Organophosphate
- Original post
- Out of print
- Overall Position
- Overland Park, Kansas
- Overpowered (game balance)
- Publications Office of the European Union
- Shakespeare in Original Pronunciation
- St Peter's School, York