| Abbreviation | Definition |
|---|---|
| UMA | United Military Alliance |
| UMD | Use Magic Device |
| UN | United Network |
| UNI | Unicorn Nervana Institute |
| UNR | United Nations of Retribution |
| UNSC | United Nationals Space Corps |
| UNSC | United Nations Space Command |
| UNSF | United Nations Space Force |
| UOP | University Of Planet |
| UQV | Ultimate Questioner's Vanity Theory |
| URC | United Runescape Clans |
| URPD | United Regions Political Department |
| USAF | United System Administrators Force |
| USB | Unstable Synthetic Brain |
| USC | United Sol Confederation |
| USF | Universal Space Federation |
| USM | Underground Soldierz Militia |
| USNE | United States of the New East |
| USS | United Star Ship |
| USS | United States Spaceship |