| Abbreviation | Definition |
|---|---|
| OR | Operating room |
| OR | Oriented |
| ORB | Operation Reconstructive Baby |
| ORCC | Outward Rectifying Chloride Channels |
| ORIF | Open Reduction, Internal Fixation |
| ORM | Oral Rehydration Mixture |
| ORS | Oculo-Respiratory Syndrome |
| ORS | Oral Rehydration Solution |
| ORS | Orally Rehydrating Solution |
| ORS | Ovarian Remnant Syndrome |
| ORT | Operating Room Technician |
| ORT | Oral Rehydration Therapy |
| ORTH | Orthopedics |
| ORTHO | Orthopedics |
| ORTHOPHOS | Orthophosphoric Acid |
| ORV | Orthopaedic Research of Virginia |
| OS | Left eye (oculus sinister) |
| OS | Ocular Sinister |
| OS | Oculus Sinister - Left Eye |
| OS | Oral Surgery |