| Meaning | Category |
| Ariel ( Uranus satellite number 1) | Governmental->NASA |
| Geoworks U I Compiler Espire language source code file | Computing->File Extensions |
| U And I | Internet->Chat |
| Ultraviolet Imaging | Governmental->NASA |
| Umbrella, Inc. | Business->Firms |
| Unauthorized Information | Computing->Security |
| Unemployment Insurance | Business->Positions |
| Uniform Interface | Computing->Networking |
| Union Initiative | Business->General |
| Unit International | Miscellaneous->Unit Measures |
| Unit Interval | Miscellaneous->Unit Measures |
| Unit of Issue | Governmental->Military |
| United Illuminating | Business->Firms |
| University of Illinois | Academic & Science->Universities |
| Unión Interparlamentaria | International->Spanish |
| Unnumbered Information (frame) | Computing->Telecom |
| Unofficial International | Governmental->United Nations |
| Unreported Income | Governmental->US Government |
| Unsigned Index | Computing->Assembly |
| Unsigned Integer | Computing->Assembly |
| Urban Institute | Academic & Science->Universities |
| User Infrastructure | Computing->Networking |
| User Interface | Academic & Science->Electronics Computing->General Computing->Drivers |
| User interface (Sprint) | Computing->File Extensions |
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