| Abbreviation | Definition |
|---|---|
| OSM | Order of St Michael |
| OSSR | Oblates SanctisSimi Redemptoris (Oblates of the Most Holy Redeemer) |
| OSU | Ursuline Sisters of the Roman Union |
| OSV | Our Sunday Visitor |
| OT | Occult Truth |
| OT | Old Testament |
| OT | Operating Thetan |
| OTC | One True Church |
| OTM | Over The Mountain |
| OTP | Old Testament Pseudepigrapha |
| OTQ | Old Testament Question |
| OTS | Ohr Torah Stone |
| OTW | OudtestamenTisch Werkgezelschap in Nederland en België (Old Testament Society) |
| OU | Orthodox Union |
| OUHC | Old Union Holiness Church |
| OV | Order of the Virgins |
| OVBC | Ocean View Baptist Church |
| OWK | Other World Kingdom |
| OWL | Older Wiser Lutherans |
| OWL | Omnipotent Wonderful Lord |