| Abbreviation | Definition |
|---|---|
| OMK | One Man Klan |
| OML | Open Meeting Law |
| OML | Open Meetings Law |
| OMSJ | Office of Medical Scientific Justice |
| OND | Officer Next Door |
| OOB | Out On Bail |
| OOC | Out Of Control |
| OOJ | Order Of Justice |
| OP | Old Prison |
| OPA | Official Police Action |
| OPAA | Ohio Prosecuting Attorneys Association |
| OPCW | Organisation for the Prohibition of Chemical Weapons |
| OPD | Office of Public Defence |
| OPD | Orleans Public Defenders |
| OPD | Ottawa Police Department |
| OPLA | Office of the Principal Legal Advisor |
| OPLA | Oregon Patent Law Association |
| OPLB | Office Public |
| OPLC | Ohio Poverty Law Center |
| OPLF | Oppedahl Patent Law Firm |