| Abbreviation | Definition |
|---|---|
| OLCC | Our Lord's Community Church |
| OLLC | Our Lord's Lutheran Church |
| OLMM | Our Lady of the Miraculous Medal (Hampton, NH) |
| OMPC | Oak Mountain Presbyterian Church |
| ONAC | Oklevueha Native American Church |
| ONCD | Orthodox Natural Church Development |
| OPC | Orthodox Presbyterian Church |
| OPCC | Overland Park Christian Church |
| OPPC | Orchard Park Presbyterian Church |
| OPPC | Overlake Park Presbyterian Church |
| OPWC | Orchard Park Wesleyan Church |
| ORBC | Oak Ridge Baptist Church |
| ORBC | Ovilla Road Baptist Church |
| ORCN | Orchard Ridge Church of the Nazarene |
| ORCN | Ovilla Road Church of the Nazarene |
| OREC | Oromo Resurrection Evangelical Church |
| ORPC | Orchard Road Presbyterian Church |
| OSBC | Ocean Shores Baptist Church |
| OSBC | Ocean State Baptist Church |
| OSLC | Our Savior Lutheran Church |