OWS
- Bellevue, Washington
- Metasyntax
- Occupy Wall Street
- Oily water separator
- Oil–water separator
- Open Geospatial Consortium
- Open Whisper Systems
- Open Window School
- Open water swimming
- Operation Warp Speed
- Opioid dependence
- Order of World Scouts
- Oritsé Williams
- Overhead Weapon Station
- Royal Watercolour Society
- Weather ship