| OPP | osmotic pressure of plasma; oxygen partial pressure |
|---|---|
| ORM | orosomucoid; other regulated material; oxygen ratio monitor |
| ORMC | oxygen ratio monitor controller |
| ORS | olfactory reference syndrome; oral rehydration solution; oral surgery, oral surgeon; Orthopaedic Res... |
| OS | left eye [Lat. oculus sinister]; occipitosacral; occupational safety; office surgery; Omenn syndrome... |