| Abbreviation | Definition |
|---|---|
| ONPS | Oklahoma Native Plant Society |
| ONS | Oriental Numismatic Society |
| ONTA | Organizacin de Nematlogos de los Trpicos Americanos |
| ONTA | Organización de Nematólogos de los Trópicos Americanos |
| OOPS | Olympia Organ Preservation Society |
| OOPS | Onslow Outdoor Painters Society |
| OOPS | Oregon Ocean Paddling Society |
| OOS | Ohio Ophthalmological Society |
| OOS | Ohio Ornithological Society |
| OPAS | Oaks Performing Arts Society |
| OPAS | Ohio Plein Air Society |
| OPAS | Olympic Peninsula Audubon Society |
| OPAS | Ontario Plein Air Society |
| OPHS | Olympic Peninsula Humane Society |
| OPMS | Orleans Parish Medical Society |
| OPS | Oceanic Preservation Society |
| OPS | Overdose Prevention Society |
| ORAS | Oil Region Astronomical Society |
| ORCS | Organic Reactions Catalysis Society |
| ORHS | Oconee Regional Humane Society |