| Abbreviation | Definition |
|---|---|
| ORAM | Organisational Readiness Assurance Model |
| OS | left eyeoculus sinister |
| OS | left eye–oculus sinister |
| OS | mouth (os) |
| OS | obese strain |
| OS | observational study |
| OS | occupational safety |
| OS | office surgery |
| OS | oligosaccharide |
| OS | Omenn syndrome |
| OS | opening snap |
| OS | Opitz syndrome |
| OS | oral solution |
| OS | organ-specific |
| OS | Osgood-Schlatter |
| OS | osteosarcoma |
| OS | osteosclerosis |
| OS | outer segment |
| OS | overlap syndrome |
| OS | oxidative stress |