| OOIC | | Out of Idle Curiosity |
| OOIE | | Object-Oriented Information Engineering |
| OOL | | out of line |
| OOL | | out of luck |
| oomp | | Obnoxious Overzealous Male Parent |
| ooo | | out of office |
| ooo | | Out Of Order |
| ooo | | out of the office |
| oop | | object oriented programming |
| oop | | out of power |
| oop | | out of print |
| OOS | | Out of Stock |
| OOSOOM | | Out Of Sight Out Of Mind |
| OOSOOM | | Out Of Sight, Out Of Mind |
| oot | | Object-Oriented Technology |
| oot | | out |
| oot | | Out Of Touch |
| oot | | out of town |
| oot | | Out on the town |
| OOTC | | Obligatory On Topic Comment |
| OOTD | | one of these days |
| OOTFPITF | | Out of the frying pan into the fire |
| OOTO | | Out Of The Office |
| OOTO | | out of the ofice |
| OOTQ | | Out Of The Question |
| OOTT | | Out on the town |
| ootw | | out of this world |
| opac | | on-line payment and collection |
| opac | | online public access catalogues |
| OPD | | Obnoxious Personality Disorder |
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