| Acronym | Definition |
|---|
| OO | Object Oriented (Programming) |
| OO | OpenOffice |
| OO | Olive Oil |
| OO | Peroxide (functional group) |
| OO | On Order |
| OO | Over and Out |
| OO | Ozzy Osbourne |
| OO | Oval Office |
| OO | Owner Operator (trucking industry; also seen as O/O) |
| OO | Operations Officer |
| OO | Owner-Occupied (real estate) |
| OO | Sky West Airlines |
| OO | Official Observer (amateur radio) |
| OO | Optimum Online |
| OO | Original Oratory |
| OO | Officers Only |
| OO | Ombudsman's Office |
| OO | Osteoid Osteoma |
| OO | Obiettivi Operativi |
| OO | Ordering Officer |
| OO | Operator Office (trunks) |
| OO | Ophthalmic Optician |
| OO | Old Oakhamian |
| OO | Optimistic Orators (Toastmasters Club) |
| OO | Onderling Onafhankelijk (Dutch) |