| U | Uranium |
| UAProf | User Agent Profile |
| UART | Universal Asynchronous Reciever/Transmitter |
| UCF | Universal Conduction Fluctuations |
| UCL | Upper confidence limit; Upper control limit |
| UDDI | Universal Description, Discovery and Integration |
| UDP | User Datagram Protocol |
| UEL | Upper explosive limit |
| UF | Ultra-Filtration |
| UFL | Upper Flammable Limit |
| UFPT | Ultra Fine Pitch Technology |
| UHB-LED | Ultra-High Brightness LED |
| UHF | Ultra High Frequency |
| UHP | Ultra High Purity |
| UHV | Ultra High Vacuum |
| UHV | Ultra high voltage |
| UI | User Interface |
| UIA | Universal Information Appliance |
| UID | User IDentification |
| UIM | User Identification Module |
| UJT | Uni Junction transistor |
| ULA | Uncommitted logic array |
| ULEV | Ultra Low Emission Vehicle |
| ULPA | Ultra-low particulate air |
| ULSI | Ultra Large Scale Integrated (circuit) |
| UMID | Unique Material IDentifier |
| UML | Unified Modeling Language |
| UMPS | Modeling language for CPU cores |
| UMS | Universal Messaging platform |
| UMTS | Universal Mobile Telecommunications Service |
| UPH | Units per hour |
| UPI | Universal Programmable Peripheral Interface |
| UPS | Ultraviolet Photoelectron Spectroscopy |
| UPS | Uninterrupted Power Supply |
| UPW | UltraPure Water |
| URI | Uniform Resource Identifier |
| URL | Uniform Resource Locater |
| USART | Universal Synchronous/Asynchronous Receiver/Transmitter |
| USB | Universal Serial Bus |
| USG | Undoped Silicate Glass |
| USIC | User-Specific Integrated Circuit |
| USIS | United States Information Service |
| USOP | Ultra small outline package |
| UTF | Unicode Transformation Format |
| UTP | Unshielded Twisted Pair |
| UTPT | Unshielded Twisted Pair Transceiver |
| UTQFP | Ultra-Thin Quad Flat-Pack |
| UTRAN | UMTS Terrestrial Radio Access Network |
| UTS | Ultra-Thin Silicon |
| UTT | Unattenuated |
| UTW | Ultra-Thin Window for EDS detectors in TEMs |
| UUT | Unit Under Test |
| UV | Ultra Violet |
| UVF | UnVerified Failure |
| UV-PROM | Ultra Violet Programmable Read Only Memory |
| UWB | Ultra WideBand |
| U/S | UltraSonic |
