| U/S | Upstream 
| Others |
| U/S | Urine Specimun
| Others |
| U/T/D | Under Trust Dated
| Others |
| U/V | Under Voltage
| Others |
| U/W | Used with
| Others |
| U/WB | Unit of Whole Blood
| Others |
| U07.1 | Deaths from lab-confirmed SARS-CoV-2 infection
| Others |
| U07.2 | Deaths from clinically or epidemiologically diagnosed COVID-19 without lab-confirmed SARS-CoV-2 infection
| Others |
| U10 | Under 10 League
| Others |
| U17CC | Under Seventeen Car Club
| Others |
| U18 | Under Eighteen
| Others |
| U2 | You Too
| Others |
| U20 | Under20
| Others |
| U2A | User to Application
| Others |
| U2B | User to Business
| Others |
| U2C | User to Content
| Others |
| U2D | User to Data
| Others |
| U2E | Usb to Ethernet
| Others |
| U2F | Universal 2nd Factor
| Others |
| U2F | Universal Second Factor
| Others |
| U2I | Usb to Ide
| Others |
| U2I | User to Interface
| Others |
| U2L | Under Two Liter
| Others |
| U2N | User to Network
| Others |
| U2NI | User to Network Interface
| Others |
| U2OB | User to Online Buying
| Others |
| U2P | User to Provider
| Others |
| U2R | User to Root
| Others |
| U2S | Usb to Serial
| Others |
| U2S | User to System
| Others |
| U2TC | Under Two Liter Touring Car
| Others |
| U2U | Unit to Unit
| Others |
| U2U | Usb to Usb
| Others |
| U2U | User to User
| Others |
| U2V | User to Vehicle
| Others |
| U2W | Ultra 2 Wide
| Others |
| U2Y | Up To You
| Others |
| U40 | Phentermine Hydrochloride pill imprint
| Others |
| U4A | Ubuntu for Android
| Others |
| U4A | UnInstaller archive
| Others |
| U4A | Usenet For All
| Others |
| U4B | Urban 4wd Buggy
| Others |
| U4E | Yours ForEver
| Others |
| U4EA | Erowid 4-Methylaminorex
| Others |
| U4U | Useful For yoU?
| Others |
| U4WD | United Four Wheel Drive
| Others |
| U4WD | University of Four Wheel Drive
| Others |
| U4WD | Utah Four Wheel Drive
| Others |
| U4WDA | United Four Wheel Drive Association
| Others |
| U4WDA | Utah Four Wheel Drive Association
| Others |