| U/L | Uplink |
| UAH | University of Alabama, Huntsville |
| UART | Universal Asynchronous Receiver/Transmitter |
| UAV | Unmanned Aerial Vehicle |
| UC | Use Case |
| UCAR | University Corporation for Atmospheric Research |
| UDF | Unit Development Folder |
| UDF | Universal Disk Format (used for CDs, DVDs, etc.) |
| UET | User Education and Training |
| UHF | Ultra High Frequency |
| UI | User Interface |
| UIID | Unique Instrument Interface Document |
| UIM | Unified Infrastructure Management |
| UL | Underwriters Laboratory |
| ULA | Unique Local Address |
| ULA | United Launch Alliance |
| ULDL | Uplink/Downlink |
| ULST | Uniform Low Stratus Test (cloud detection test) |
| ULW | Upward Longwave radiation, refers to the GOES-R product Upward Longwave Radiation: Surface |
| UMBC | University of Maryland Baltimore County |
| UMD | University of Maryland |
| UND | University of North Dakota |
| UNH | University of New Hampshire |
| UPN | Unique Project Number |
| UPS | Uninterruptible Power Supply |
| UPS | Unique Payload Services |
| URI | Unique Resource Identifier |
| URL | Uniform Resource Locator |
| US | Under Secretary for Oceans and Atmosphere |
| US-CERT | United States Computer Emergency Readiness Team |
| USAF | United States Air Force |
| USB | Universal Serial Bus |
| USC | Umbilical Support Console |
| USC | United States Code |
| USF | User Services Functionality |
| USFS | United States Forest Service |
| USGS | United States Geological Survey |
| USML | United States Munitions List |
| USN | United States Navy |
| USN | Universal Space Network |
| USN/NEN | Universal Space Network/Near Earth Network |
| USSPACECOM | United States Space Command |
| UTC | Coordinated Universal Time |
| UTF | Unicode Transformation Format |
| UTR | Unit Test Review |
| UV | Ultraviolet |
| UW | University of Wisconsin |
| µsec | micro-seconds |