| O | Opponent | - | ISO Country Codes |
| O | Over | - | ISO Country Codes |
| O4U | Only For You | - | ISO Country Codes |
| OAO | Over And Out | - | ISO Country Codes |
| OATUS | On A Totally Unrelated Subject | - | ISO Country Codes |
| OAUS | On An Unrelated Subject | - | ISO Country Codes |
| OB | Obligatory | - | ISO Country Codes |
| OBE | Overcome By Events | - | ISO Country Codes |
| OBO | Or Best Offer | - | ISO Country Codes |
| OBTW | Oh By The Way | - | ISO Country Codes |
| OBX | Old Battle Axe | - | ISO Country Codes |
| OC | Original Character | - | ISO Country Codes |
| OC | Own Character | - | ISO Country Codes |
| OCD | Obsessive Compulsive Disorder | - | ISO Country Codes |
| ODTAA | One Damn Thing After Another | - | ISO Country Codes |
| OIC | Oh, I See | - | ISO Country Codes |
| OICU812 | Oh I See, You Ate One Too | - | ISO Country Codes |
| OK | Okay | - | ISO Country Codes |
| OK | All Correct | - | ISO Country Codes |
| OL | Old Lady | - | ISO Country Codes |
| OLL | OnLine Love | - | ISO Country Codes |
| OLN | OnLine Netiquette | - | ISO Country Codes |
| OM | Old Man | - | ISO Country Codes |
| OMB | Oh My Buddha | - | ISO Country Codes |
| OMDB | Over My Dead Body | - | ISO Country Codes |
| OMFG | Oh My F*cking God | - | ISO Country Codes |
| OMG | Oh My God | - | ISO Country Codes |
| OMIK | Open Mouth, Insert Keyboard | - | ISO Country Codes |
| OML | Oh My Lord | - | ISO Country Codes |
| OMW | On My Way | - | ISO Country Codes |
| ONID | Oh No I Didn't | - | ISO Country Codes |
| ONNA | Oh No, Not Again | - | ISO Country Codes |
| ONNTA | Oh No, Not This Again | - | ISO Country Codes |
| ONUD | Oh No You Didn't | - | ISO Country Codes |
| ONUD | Oh No You Don't | - | ISO Country Codes |
| OO | Over And Out | - | ISO Country Codes |
| OOAK | One Of A Kind | - | ISO Country Codes |
| OOC | Out Of Character | - | ISO Country Codes |
| OOC | Out Of Control | - | ISO Country Codes |
| OOF | Out Of Facility | - | ISO Country Codes |
| OOI | Out Of Interest | - | ISO Country Codes |
| OOO | Out Of Office | - | ISO Country Codes |
| OOS | Out Of Stock | - | ISO Country Codes |
| OOTB | Out Of The Blue | - | ISO Country Codes |
| OOTB | Out Of The Box | - | ISO Country Codes |
| OOTC | Obligatory On Topic Comment | - | ISO Country Codes |
| OSIF | Oh Sh*t I Forgot | - | ISO Country Codes |
| OSINTOT | Oh Sh*t I Never Thought Of That | - | ISO Country Codes |
| OST | On Second Thought | - | ISO Country Codes |
| OT | Off Topic | - | ISO Country Codes |
| OTASOIC | Owing To A Slight Oversight In Construction | - | ISO Country Codes |
| OTC | Over The Counter | - | ISO Country Codes |
| OTF | Off The Floor | - | ISO Country Codes |
| OTF | On The Phone (Fone) | - | ISO Country Codes |
| OTH | Off The Hook | - | ISO Country Codes |
| OTL | Out To Lunch | - | ISO Country Codes |
| OTOH | On The Other Hand | - | ISO Country Codes |
| OTP | On The Phone | - | ISO Country Codes |
| OTT | Over The Top | - | ISO Country Codes |
| OTTOMH | Off The Top Of My Head | - | ISO Country Codes |
| OTW | Off The Wall | - | ISO Country Codes |
| OUSU | Oh, You Shut Up | - | ISO Country Codes |
| OWTTE | Or Words To That Effect | - | ISO Country Codes |
| OZ | Australia | - | ISO Country Codes |
