| UA | User agent |
| UADSL | Universal ADSL |
| UAK | User-authentication key |
| UART | Universal Asynchronous Receiver Transmitter |
| UAV | Unmanned Aerial Vehicle |
| UAWG | Universal ADSL Working Group |
| UBR | Unspecified bit rate |
| UBT | Ubiquitous bus technology |
| UCC | Uniform Code Council |
| UCD | Uplink Channel Descriptor |
| UCP | Universal computer protocol |
| UCS | Uniform communication standard |
| UDP | User Datagram Protocol |
| UE | User Equipment |
| UGS | Unsolicited Frant Service |
| UHF | Ultra High Frequency |
| UI | User interface |
| UIM | User Identity Module |
| ULC | Ultra Low Cost |
| ULH | Ultra-long-haul |
| ULP | Ultra Low Power |
| ULS | Universal Licensing System |
| UM | Unlicensed Mobile Access |
| UMB | Ultra Mobile Broadband |
| UML | Unified modeling language |
| UMTS | Universal Mobile Telecommunications System |
| UMTS | Universal Mobile Telecommunications Service |
| UMTS | Universal Mobile Telecommunications System |
| UN | United Nations |
| UNE | Unbundled network element |
| UNH-IOL | University of New Hampshire-Interoperability Laboratory |
| UNI | User network interface |
| UNII | Unlicensed National Information Infrastructure |
| UOL | Unbundled optical loop |
| UPC | Uplink Power Control /Usage parameter control |
| UPI | User personal identification |
| UPSR | Unidirectional Path-Switched Ring |
| URI | Uniform Resource Identifier |
| URL | Universal Resource Locator |
| USART | Universal Synchronous/asynchronous Receiver/Transmitter |
| USB | Universal Serial Bus |
| USIF | Universal Serial Interface |
| USTA | United States Telephone Association |
| Utopia | Universal Test and Operations Interface for ATM |
| UTRA | UMTS Terrestrial Radio Access |
| UTS | Universal Telephone Service |
| UWB | Ultra-Wideband |
| UWB SRR | Ultra Wideband Short Range Radar |