| Abbreviation | Definition |
|---|---|
| TZC | Time Zone Converter |
| TZD | Time Zone Designator |
| TZI | Time Zone Information |
| TZN | Time ZoNe |
| TZN | Time Zone Name |
| UCT | INCORRECT abbreviation for Coordinated Universal Time (see UTC) |
| USDOT | United States Department of Transportation |
| USNO | United States Naval Observatory |
| USNOMC | United States Naval Observatory Master Clock |
| USTZ | United States Time Zones |
| UT | Universal Time (now considered as UT0) |
| UT1 | Universal Time (with polar motion taken into account) |
| UT2 | Universal Time (with polar motion and seasonal 'slurring' of the Earth's rotation taken into account) |
| UTC | Coordinated Universal Time (Temps Universel Coordonné) |
| UTC | Coordinated Universal Time (Temps Universel Coordonné) [language-independent abbreviation, French: BIPM-verified.] |
| UTZ | Greenland Western Standard Time [UTC - 0300] |
| UYT | Uruguay Time [UTC - 0300] |
| UZT | Uzbekistan Time [UTC + 0500] |
| VNG | Australia Standard time and frequency radio station |
| VT | Virtual Time |