| OEF | oil immersion field; oxygen extraction fraction |
|---|---|
| OIF | observed intrinsic frequency; oil immersion field; Osteogenesis Imperfecta Foundation |
| ol | oliv olive oil [Lat. oleum olivea] |
| OR | a logical binary relation that is true if any argument is true, and false otherwise; [o]estrogen rec... |
| ORE | oil retention enema |