| U051 | UNB | Ultra Narrow Band | Wireless communication using minimal bandwidth | Used in IoT devices for low-power communication |
| U052 | UNC | Unified National Coarse | Standard screw thread | Bolts and fasteners in mechanical engineering |
| U053 | UND | University of Notre Dame | Educational institution | STEM research and sports programs |
| U054 | UNEP | United Nations Environment Programme | Global environmental agency | Climate action and sustainability projects |
| U055 | UNF | Unified National Fine | Standard screw thread | Used in precision mechanical parts |
| U056 | UNH | University of New Hampshire | Research university | Marine biology and computer science programs |
| U057 | UNI | University Network Interface | Network connection standard | Campus networking infrastructure |
| U058 | UNIC | United Nations Information Centre | UN outreach office | Disseminating UN publications |
| U059 | UNICORE | Uniform Interface to Computing Resources | Grid computing middleware | Managing distributed scientific computing resources |
| U060 | UNIX | Uniplexed Information and Computing System | Multiuser operating system | Server OS for web and research applications |
| U061 | UNIVAC | Universal Automatic Computer | Early commercial computer | Mainframe computing in the 1950s |
| U062 | UNM | University of New Mexico | Research institution | Engineering and medical research programs |
| U063 | UNO | United Nations Organization | Global intergovernmental organization | Peacekeeping and humanitarian missions |
| U064 | UNOS | United Network for Organ Sharing | Organization managing organ transplants | Coordinating kidney and liver transplants |
| U065 | UNR | University of Nevada, Reno | Higher education and research | Engineering and environmental studies |
| U066 | UNRWA | United Nations Relief and Works Agency | Humanitarian support for refugees | Providing education and healthcare in Palestine |
| U067 | UNSC | United Nations Security Council | UN body maintaining peace and security | Sanction decisions and peacekeeping mandates |
| U068 | UNSW | University of New South Wales | Leading Australian university | Engineering, law, and medical research |
| U069 | UNV | United Nations Volunteers | Volunteer program supporting UN initiatives | Deployment in disaster relief operations |
| U070 | UNWTO | United Nations World Tourism Organization | Agency promoting responsible tourism | Tourism policy guidance and global statistics |
| U071 | UOA | University of Adelaide | Australian university | Research in agriculture and engineering |
| U072 | UOC | University of California | University system with multiple campuses | Berkeley, Los Angeles, San Diego campuses |
| U073 | UOM | Unit of Measure | Standardized measurement unit | Kilogram, meter, or liter in industrial processes |
| U074 | UON | University of Nairobi | Higher education institution in Kenya | Engineering, medical, and IT programs |
| U075 | UP | Uninterruptible Power | Emergency power backup system | Industrial UPS systems |
| U076 | UPF | Ultraviolet Protection Factor | Clothing rating against UV rays | Sun-protective apparel |
| U077 | UPSC | Union Public Service Commission | Government agency for civil services exams | Conducting IAS and IPS exams in India |
| U078 | UR | Upper Receiver | Part of a firearm or mechanical assembly | AR-15 rifle component |
| U079 | URC | Universal Remote Control | Device controlling multiple electronics | TV, stereo, and smart home devices |
| U080 | URD | Underground Residential Distribution | Electrical distribution system | Power supply to residential areas |
| U081 | URI | Uniform Resource Identifier | Identifies resources on the Internet | Includes URLs and URNs for web resources |
| U082 | URL | Uniform Resource Locator | Web page or file address | Example: https://www.openai.com |
| U083 | URN | Uniform Resource Name | Persistent identifier independent of location | ISBNs for books |
| U084 | URP | Uniform Resource Policy | Rules for accessing digital resources | Network access control in IT systems |
| U085 | US | United States | Country in North America | National reference in politics and geography |
| U086 | USA | United States of America | Official country name | Government and international documentation |
| U087 | USB | Universal Serial Bus | Standard for connecting peripherals | USB drives, keyboards, and printers |
| U088 | USC | University of Southern California | Private research university | Programs in film, engineering, and business |
| U089 | USD | United States Dollar | Official US currency | Pricing, banking, and international trade |
| U090 | USEPA | United States Environmental Protection Agency | Federal environmental protection agency | Air, water, and soil quality regulations |
| U091 | USGS | United States Geological Survey | Scientific agency monitoring natural resources | Earthquake, volcano, and geological studies |
| U092 | USN | United States Navy | Branch of US armed forces | Naval operations and defense missions |
| U093 | USO | United Service Organizations | Support for US military personnel | Entertainment and welfare programs for troops |
| U094 | USS | United States Ship | Ship prefix for naval vessels | USS Enterprise aircraft carrier |
| U095 | UST | Underground Storage Tank | Subsurface storage for liquids | Fuel storage at gas stations |
| U096 | UTF | Unicode Transformation Format | Standard for encoding Unicode characters | Text encoding in software applications |
| U097 | UTP | Unshielded Twisted Pair | Type of network cabling | Ethernet connections in LANs |
| U098 | UTC | Coordinated Universal Time | Primary time standard worldwide | Scheduling international events |
| U099 | UTI | Urinary Tract Infection | Bacterial infection in urinary system | Diagnosis in medical clinics |
| U100 | UAV | Unmanned Aerial Vehicle | Remotely operated aircraft | Used for photography, mapping, or surveillance |
| U101 | UHF | Ultra High Frequency | Radio frequency range 300 MHz–3 GHz | Television broadcasting and Wi-Fi |
| U102 | UHV | Ultra High Voltage | Very high electrical transmission voltage | Power grid transmission lines |
| U103 | UI | User Interface | Interaction space between user and system | Software apps and websites |
| U104 | UID | Unique Identifier | Distinct code identifying an object or record | Device IDs and national IDs |
| U105 | UIC | International Union of Railways | Railway organization standardizing systems | Rail transport interoperability |
| U106 | UIM | User Identity Module | SIM card technology in mobile devices | Mobile network authentication |
| U107 | UIN | Unique Identification Number | Individual ID in systems | Tax or national ID number |
| U108 | UIO | User Input/Output | Interaction mechanism with system | Keyboard and monitor interfaces |
| U109 | UP | Upper Port | Designated upper connection in a device | Plumbing or network port reference |
| U110 | UPA | United Progressive Alliance | Political coalition | Governance and policy reference in India |
| U111 | UPG | User Profile Group | Categorization of users in systems | Access control in enterprise software |
| U112 | UPI | Unified Payments Interface | Real-time payment system in India | Mobile banking transactions |
| U113 | UPF | Ultraviolet Protection Factor | Rating for UV protective fabrics | Outdoor clothing specifications |
| U114 | UPS | Uninterruptible Power Supply | Emergency power for electronic devices | Backup for servers and computers |
| U115 | UR | Upper Receiver | Component in firearms | AR-type rifle assemblies |
| U116 | URA | Urban Redevelopment Authority | Government body managing urban planning | City redevelopment projects |
| U117 | URC | Universal Remote Control | Device controlling multiple electronic systems | TV, AC, and audio system control |
| U118 | URG | Urgent | Label indicating high priority | Medical or shipping priority handling |
| U119 | URN | Uniform Resource Name | Persistent resource identifier | Digital library or ISBN reference |
| U120 | URS | User Requirement Specification | Document detailing system requirements | Software or engineering project specifications |
| U121 | URT | Upper Respiratory Tract | Part of human respiratory system | Medical diagnosis of sinus infections |
| U122 | USB | Universal Serial Bus | Standard communication interface | Connecting mouse or external drive |
| U123 | USDT | United States Dollar Tether | Cryptocurrency pegged to USD | Crypto exchange trading |
| U124 | USE | User System Environment | Configured system context | Software installation path reference |
| U125 | USI | Unique Student Identifier | National student ID system | Academic record management |
| U126 | USM | Ultrasonic Motor | Motor using ultrasonic vibration | Camera lens focusing systems |
| U127 | USN | United States Navy | Naval branch of the US military | Fleet operations and defense |
| U128 | USP | United States Pharmacopeia | Standards for medicines and supplements | Pharmaceutical quality control |
| U129 | USR | User | Generic term for system user | Login and access control systems |
| U130 | UST | Underground Storage Tank | Storage container below ground | Fuel or chemical storage systems |
| U131 | UTA | Utah Transit Authority | Regional transportation service | Public bus and rail transport |
| U132 | UTC | Coordinated Universal Time | Global time standard | Synchronizing servers and global events |
| U133 | UTI | Urinary Tract Infection | Bacterial infection of urinary system | Clinical diagnosis and treatment |
| U134 | UTP | Unshielded Twisted Pair | Common Ethernet cabling type | Local area network setup |
| U135 | UTS | Ultimate Tensile Strength | Maximum material stress before failure | Engineering material testing |
| U136 | UUV | Unmanned Underwater Vehicle | Autonomous underwater vehicle | Oceanographic research and mapping |
| U137 | UV | Ultraviolet | Type of electromagnetic radiation | Sterilization lamps and UV index |
| U138 | UVB | Ultraviolet B | Medium-wave UV radiation | Sunburn protection measurement |
| U139 | UVC | Ultraviolet C | Short-wave UV radiation | Germicidal lamps in labs |
| U140 | UVI | Ultraviolet Index | Measure of UV radiation intensity | Health advisory for sun exposure |
| U141 | UWB | Ultra Wide Band | Wireless communication with wide frequency | High-speed data transmission |
| U142 | UWT | Underwater Welding Technology | Techniques for welding underwater | Offshore oil rig maintenance |
| U143 | UX | User Experience | Overall experience of interacting with a system | Website or app usability design |
| U144 | UXL | Ultra Extended Life | Product lifespan specification | Long-life industrial batteries |
| U145 | UZ | Uzbekistan | Country in Central Asia | Country code and international reference |
| U146 | UZI | Universal Zone Identifier | Location identifier in systems | GIS mapping and tracking |
| U147 | UZN | Ultra-Zone Network | High-speed network architecture | Data center connectivity |
| U148 | UZD | Unmanned Zone Device | Autonomous monitoring device | Border surveillance drones |
| U149 | UZE | Ultra Zero Emission | Vehicle or system emission standard | Electric vehicles and renewable energy |
| U150 | UZF | Unsaturated Zone Flow | Groundwater hydrology term | Environmental and water studies |
| U151 | UZH | University of Zurich | Research university | Studies in medicine, economics, and science |
| U152 | UZI | Uziel | Firearm designation | Submachine gun historical reference |
| U153 | UZP | Urban Zoning Plan | City planning framework | Municipal urban development projects |
| U154 | UZV | Ultra Zone Voltage | Electrical system voltage specification | Power grid and industrial systems |
| U155 | UZZ | Universal Zone Z | Generalized area code reference | GIS or zoning system |
| U156 | UAF | University of Alaska Fairbanks | Public research university | Arctic research and engineering |
| U157 | UAM | Urban Air Mobility | Air transport solutions in cities | Flying taxi or drone delivery systems |
| U158 | UAS | Unmanned Aircraft System | Complete system including UAV and control | Military and civilian drone operations |
| U159 | UB | Upper Bound | Maximum limit in mathematics or computation | Defining constraints in algorithms |
| U160 | UBC | University of British Columbia | Canadian research university | Studies in medicine, engineering, and law |
| U161 | UBD | Universal Beam Design | Standard structural beam calculation | Civil and mechanical engineering |
| U162 | UBM | User Behavior Modeling | Analysis of user actions for insights | Web analytics and app usage tracking |
| U163 | UBX | Universal Box | Standard enclosure or container | Electronics or shipping packaging |
| U164 | UC | Unified Communications | Integrated communication services | VoIP, video conferencing, and messaging |
| U165 | UCA | Universal City Airport | Aviation facility designation | Airport identification code |
| U166 | UCB | University of California, Berkeley | Leading research university | Engineering and computer science programs |
| U167 | UCC | Uniform Commercial Code | Standardized commercial law | Regulating sales, contracts, and commerce |
| U168 | UCD | User-Centered Design | Design process focusing on users | Website and application UI/UX |
| U169 | UCE | University College of Engineering | Engineering education institute | Academic programs and research |
| U170 | UCI | University of California, Irvine | Research university | Medical, engineering, and IT studies |
| U171 | UCL | University College London | UK research university | Science, engineering, and arts programs |
| U172 | UCM | Unified Communications Manager | Cisco platform for managing communications | VoIP and video conference management |
| U173 | UCN | University College of the North | Canadian post-secondary institution | Academic and vocational training |
| U174 | UCQ | Ultra Clean Quality | Standard for high-purity products | Semiconductor or pharmaceutical manufacturing |
| U175 | UCR | University of California, Riverside | Public research university | Agricultural, engineering, and IT research |
| U176 | UCS | Universal Character Set | International encoding standard | Basis for Unicode implementation |
| U177 | UCSD | University of California, San Diego | Public research university | Marine biology, engineering, and medicine |
| U178 | UCT | University of Cape Town | Leading African research university | Engineering, medical, and business programs |
| U179 | UCV | Universal Control Valve | Valve regulating system flow | Industrial automation and water supply |
| U180 | UCX | Unified Computing Experience | Integrated computing platform | Enterprise IT systems |
| U181 | UD | User Datagram | Packet in networking without acknowledgment | UDP-based applications |
| U182 | UDA | Urban Development Authority | Government urban planning body | City infrastructure and zoning |
| U183 | UDC | User Defined Class | Custom class in programming | Object-oriented software development |
| U184 | UDF | Universal Disk Format | File system standard | Used in DVDs and optical media |
| U185 | UDG | Ultra Deep Gas | Gas extraction from extreme depths | Offshore oil and gas drilling |
| U186 | UDI | Unique Device Identifier | ID for medical devices | FDA compliance and device tracking |
| U187 | UDL | Universal Design for Learning | Educational framework for accessibility | Inclusive classroom design |
| U188 | UDM | User Data Management | Handling user information | Database and cloud services |
| U189 | UDN | User Datagram Network | Network using UDP for data transfer | Streaming and real-time applications |
| U190 | UDO | Universal Data Object | Data structure for integration | Software interoperability |
| U191 | UDP | User Datagram Protocol | Lightweight network protocol | Streaming video and online gaming |
| U192 | UDR | User Defined Routing | Custom network routing rules | Enterprise IT network management |
| U193 | UDS | Unified Diagnostic Services | Automotive diagnostic protocol | ECU fault detection in vehicles |
| U194 | UDT | UDP-based Data Transfer | Reliable transport over UDP | File transfer systems |
| U195 | UDV | Ultra Deep Vision | Advanced imaging technology | Subsurface mapping and exploration |
| U196 | UE | User Equipment | Mobile device used by end user | Smartphone or IoT device |
| U197 | UEC | University of Electro-Communications | Japanese research university | Electronics and communications programs |
| U198 | UEM | Unified Endpoint Management | IT system for device management | Corporate laptop and mobile device administration |
| U199 | UEV | Ultra Electric Vehicle | High-performance electric vehicle | EV prototype or production model |
| U200 | UAV | Unmanned Aerial Vehicle | Remotely operated aircraft | Used for aerial photography, surveying, or delivery |