| UHS | ultimate heat sink |
| UHF | ultrahigh frequency |
| UDRPS | ultrasonic data recording and processing system |
| UT | ultrasonic testing |
| uv | ultraviolet |
| underfrequency |
| undersized |
| undervoltage |
| UL | Underwriters Laboratory |
| UBC | Uniform Building Code |
| UFC | Uniform Fire Code |
| UPC | Uniform Plumbing Code |
| UPS | uninterruptible power system |
| URI | unresolved item |
| USI | unresolved safety issue |
| UEQ | unreviewed environmental question |
| USQ | unreviewed safety question |
| upender |
| U | uranium |
| USCGS | U.S. Coast and Geodetic Survey |
| USCEA | U.S. Council for Energy Awareness |
| USGS | U.S. Geological Survey |
| VBS | vehicle barrier systems |
| v | velocity |
| VHF | very high frequency |
| VLF | very low frequency |
| VLPM | vibration and loose parts monitor |
| viz. | videlicet (namely) |
| V-notch (hardness test) |
| V | volt |
| VAR | volt amps reactive |
| V/m | volt per meter |
| VA | volt-ampere |
| Vac | volts, alternating current |
| Vdc | volts, direct current |
| vol | volume |
| VCT | volume control tank |
| vpm | volume parts per million |
| vol % or v/o | volume percent |
| v/v | volume per volume |