| Abbreviation | Definition |
|---|---|
| UMP | Useless Message Poster |
| UMS | Under My Skin |
| UMTWTM | You Mean The World To Me |
| UN | Unorganized Neophytes |
| UN | Unquestionably Nothing |
| UN | Unwritten Noses |
| UN | Ure Next |
| UN | Utter Nonsense |
| UN | Utterly Non |
| UN4TUN8 | Unfortunate |
| UNAL | You Need A Life |
| UNB | U a No- Body |
| UNC | User Name Club |
| UNG | U No Good |
| UNODIR | Unless Otherwise Directed |
| UNOIT | You Know It |
| UNS | U kNow Squat |
| UNTK | You Need to Know |
| UNZ | Unzip |
| UO | Unpopular Opinion |