| Abbreviation | Definition |
|---|---|
| UMS | Unified Modeling Language (Object Management Group) |
| UN | unacceptable |
| UNAIDS | Joint United Nations Program on HIV/AIDS |
| UNESCO | United Nations Educational, Scientific and Cultural Organization |
| UNII | Unique Ingredient Identifier |
| UNOS | United Network for Organ Sharing |
| UPLC | Ultra Performance Liquid Chromatography |
| URL | Uniform Resource Locator |
| URS | User Requirement Specification |
| US&R | Urban Search And Rescue |
| USAHA | United States Animal Health Association |
| USAMRIID | U.S. Army Medical Research Institute for Infectious Diseases |
| USAMRIID | United States Army Medical Research Institute for Infectious Diseases |
| USAN | United States Adopted Name |
| USBR | Bureau of Reclamation (U.S. Department of the Interior) |
| USFDA | United States Food and Drug Administration |
| USFS | United States Forest Service (U.S. Department of Agriculture) |
| USHIK | United States Health Information Knowledge Base |
| USOPM | United States Office of Personnel Management |
| USP | United States Pharmacopeia |