| Abbreviation | Definition |
|---|---|
| UIF | WordPerfect for Windows Long prompts for windows |
| UIH | Geoworks U I Compiler Espire header file |
| UIL | Motif UIL icon file Bitmap graphics |
| UIS | WindowBlinds Skin file |
| UKA | FIFA World Cup Game Data file |
| UKS | Microsoft Works File |
| UKX | Unreal Tournament 2003 Animation file |
| UL | ULAW Music file |
| ULD | Uploaded file information ( Procomm Plus) |
| ULT | UltraTracker Music file |
| ULX | Glulx data file |
| UMB | MemMaker Backup file |
| UND | Undefined symbols |
| UNI | Forecast Pro Datafile |
| UNI | UniMOD or MikMOD Music file |
| UNV | SDRC I-DEAS file |
| UNX | Text file containing UNIX specific information |
| UPD | Update information |
| UPF | Universal Picture Format Bitmap graphics |
| upnsuffix | User Principal Name |