| Abbreviation | Definition |
|---|---|
| OS | OStium (mouth) |
| OS | Oxygen Saturation |
| OSA | Obstructive Sleep Apnea |
| OSA | Overhead Squat Area |
| OSC | Objective Straight Chiropractic |
| OSCE | Objective Structured Clinical Examination |
| OSM | Object Space Manager |
| OSMR | oncostatin M receptor beta |
| OSQ | Overhead Squat |
| OSR | Oxidative Stress Relief |
| OST | Osmotic Shock Therapy |
| OT | Objective test |
| OT | Observing Tool |
| OT | Occupational Therapy |
| OT | Old Tuberculin |
| OT | Operating Theater |
| OT | Orthostatic Tremors |
| OTC | Ornithine Transcarbamylase Deficiency |
| OTIS | Operative Term Is Stimulate |
| OTO | Otology |