| Abbreviation | Definition |
|---|---|
| O | Orifice |
| O | Osteoarthritis |
| O&A | Odontectomy and Alveolectomy |
| O&E | Observation and Examination |
| O&P | Ova and Parasite |
| O.P. | osmotic pressure |
| o/a | old age |
| O2 | Oxygen |
| O2SAT | Oxygen SATurated hemoglobin |
| OA | Ocular Albinism |
| OA | Optical Axis |
| OA | OsteoArthritis |
| OA | Osteoarthritis, Occiput Posterior |
| OAB | Over- Active Bladder |
| OAP | OsteoArthroPathy |
| OAR | Offal And Regurgitation |
| OASIS | On-line Asperger's Syndrome Information and Support |
| OAT | Oral Appliace Therapy |
| OATS | Osteochondral Autograft Transfer System |
| OAV | Orthopaedic Associates of Virginia |