| O&O | Over And Out | |
| OAO | Over And Out | |
| OAR | On A Roll | |
| OBTW | Oh By The Way | |
| OF | Old Fart | |
| OFL | Out For Lunch | |
| OIC | Oh I See | |
| OICN | Oh, I See Now | |
| OL | Old Lady | |
| OLL | Online Love | |
| OM | Old Man | |
| OMDB | Over My Dead Body | |
| OMFG | Oh My Freaking Gosh | |
| OMG | Oh My Goodness | |
| OMOHOD | One Minute, One Hour, One Day | |
| OMW | On My Way | |
| ONNA | Oh No, Not Again | |
| ONYD | Oh No You Didn't | |
| OO | On Order | |
| OO | Openoffice | |
| OO | Over And Out | |
| OOC | Out Of Character | |
| OOTB | Out Of The Box | |
| OT | Off Topic | |
| OT | Other Topic | |
| OT | Overtime | |
| OTF | Off The Floor | |
| OTGL | On The Ground Laughing | |
| OTH | Off The Hook | |
| OTL | Out To Lunch | |
| OTOH | On The Other Hand | |
| OTP | On The Phone | |
| OTT | Over The Top | |
| OTTH | On The Third Hand | |
| OTTOMH | Off The Top Of My Head | |
| OTW | Off To Work | |
| OTW | On The Way | |
| (-: to the Emoticons :-) |
