| U.S.C. | United States Code | - | Computer Acronyms(common) |
| UA | Unequilibrated Aggregate (interplanetary Dust Particle) | - | Computer Acronyms(common) |
| UA | United Atom | - | Computer Acronyms(common) |
| UAM | Urban Airshed Model | - | Computer Acronyms(common) |
| UAM-IV | Urban Airshed Model Version IV | - | Computer Acronyms(common) |
| UAMO | Unprojected Alternant Molecular Orbital | - | Computer Acronyms(common) |
| UAP | Utilization Associated Products | - | Computer Acronyms(common) |
| UAPS | Utility Acid Precipitation Study | - | Computer Acronyms(common) |
| UAPSP | Utility Acid Precipitation Study Program | - | Computer Acronyms(common) |
| UAQI | Uniform Air Quality Index | - | Computer Acronyms(common) |
| UARP | Upper Atmospheric Research Program | - | Computer Acronyms(common) |
| UARS | Upper Atmosphere Research Satellite | - | Computer Acronyms(common) |
| UASB | Upflow Anaerobic Sludge Blanket | - | Computer Acronyms(common) |
| UASBR | Upflow Anaerobic Sludge Blanket Reactor | - | Computer Acronyms(common) |
| UATMP | Urban Air Toxics Monitoring Program | - | Computer Acronyms(common) |
| UBA | Unitarized Born Approxn. | - | Computer Acronyms(common) |
| UBD | Under-bath Decarburization | - | Computer Acronyms(common) |
| UBFF | Urey-Bradley Force Field | - | Computer Acronyms(common) |
| UBM | Under Bump Metallurgy | - | Computer Acronyms(common) |
| UBT | Urea Breath Test | - | Computer Acronyms(common) |
| UCA | Unit Cell Approximation [simulation Method] | - | Computer Acronyms(common) |
| UCAR | University Corporation For Atmospheric Research | - | Computer Acronyms(common) |
| UCAS-SCF | Unrestricted Complete Active Space Self-consistent Field | - | Computer Acronyms(common) |
| UCC | Unitary Coupled-cluster | - | Computer Acronyms(common) |
| UCC(N) | Unitary Coupled-cluster [truncated To Nth Order] | - | Computer Acronyms(common) |
| UCCD | (spin) Unrestricted Coupled Cluster (with) Double (excitations) | - | Computer Acronyms(common) |
| UCCSD | (spin) Unrestricted CCSD | - | Computer Acronyms(common) |
| UCDW | Ultrarelativistic Continuum Distorted Wave | - | Computer Acronyms(common) |
| UCEPA | Unitary Coupled Electron Pair Approximation | - | Computer Acronyms(common) |
| UCG | Underground Coal Gasification | - | Computer Acronyms(common) |
| UCHF | Uncoupled Hartree-Fock | - | Computer Acronyms(common) |
| UCHFPT | Uncoupled Hartree-Fock Perturbation Theory | - | Computer Acronyms(common) |
| UCI | Ultrasonic Contact Impedance | - | Computer Acronyms(common) |
| UCID | Unrestricted CI (with) Single (and) Double (excitations) | - | Computer Acronyms(common) |
| UCL | Upper Confidence Limit | - | Computer Acronyms(common) |
| UCM | Unresolved Complex Mixt. | - | Computer Acronyms(common) |
| UCMP | Unrestricted Compact Model Potential | - | Computer Acronyms(common) |
| UCMR | Unregulated Contaminant Monitoring Regulation | - | Computer Acronyms(common) |
| UCP | Uncoupling Protein | - | Computer Acronyms(common) |
| UCS | Unconfined Compressive Strength | - | Computer Acronyms(common) |
| UCST | Upper Critical Solution Temperature | - | Computer Acronyms(common) |
| UCT | University Of Cape Town | - | Computer Acronyms(common) |
| UDDS | Urban Dynamometer Driving Schedule | - | Computer Acronyms(common) |
| UDF | Unrestricted Dirac-Fock | - | Computer Acronyms(common) |
| UDI | Utility Data Institute (power Generation) | - | Computer Acronyms(common) |
| UDMH | Unsymmetrical Dimethyl Hydrazine (Alar Metabolite) | - | Computer Acronyms(common) |
| UDP | Uridine 5'-diphosphate | - | Computer Acronyms(common) |
| UDRI | University Of Dayton Research Institute | - | Computer Acronyms(common) |
| UDWA | Unitarized Distorted-wave Approximation | - | Computer Acronyms(common) |
| UDWBA | Unitarized Disorted Wave Born Approxn. (for Scattering) | - | Computer Acronyms(common) |
| UEATC | European Union For Technical Agreements In Construction (French; L'Union Europeenne Pour L'Agrement Technique Dans La Construc | - | Computer Acronyms(common) |
| UEBS | Unitarized Eikonal Born Series (in Electron-atom Scattering) | - | Computer Acronyms(common) |
| UEGO | Universal Exhaust Gas Oxygen Sensor | - | Computer Acronyms(common) |
| UEL | Upper Explosive Limit | - | Computer Acronyms(common) |
| UERPIC | Underground Excavation And Rock Properties Information Center | - | Computer Acronyms(common) |
| UF | Ultrafiltration (water Treatment) | - | Computer Acronyms(common) |
| UF | Uncertainty Factor (in Oral RfD) | - | Computer Acronyms(common) |
| UFC | Uniform Fire Code | - | Computer Acronyms(common) |
| UFF | Universal Force Field | - | Computer Acronyms(common) |
| UFFI | Urea-formaldehyde Foam Insulation | - | Computer Acronyms(common) |
| UFG | Ultrafine Grained | - | Computer Acronyms(common) |
| UFL | Upper Flammable Limit | - | Computer Acronyms(common) |
| UFM | Ultrasonic Force Microscopy | - | Computer Acronyms(common) |
| UFP | Ultrafine Particles | - | Computer Acronyms(common) |
| UGF | Unitary-group Formulation (in Many-body Quantum Theory) | - | Computer Acronyms(common) |
| UGLCC | Upper Great Lakes Connecting Channels | - | Computer Acronyms(common) |
| UHC | Unburned Hydrocarbons | - | Computer Acronyms(common) |
| UHE | Ultra-high Energy | - | Computer Acronyms(common) |
| UHF | Ultra-high Frequency | - | Computer Acronyms(common) |
| UHF | Unrestricted Hartree-Fock | - | Computer Acronyms(common) |
| UHF-AA | Unrestricted Hartree-Fock (with Spin) Annihilation | - | Computer Acronyms(common) |
| UHF-CO | Unrestricted Hartree-Fock Crystal Orbital | - | Computer Acronyms(common) |
| UHFQ | Unrestricted Hartree-Fock With Quartet Annihilation | - | Computer Acronyms(common) |
| UHFS | Unrestricted Hartree-Fock-slater | - | Computer Acronyms(common) |
| UHIPI | Ultrahigh Intensity Post-ionization | - | Computer Acronyms(common) |
| UHMPE | Ultra High Modulus Polyethylene | - | Computer Acronyms(common) |
| UHMWPE | Ultra High Molecular Weight Polyethylene | - | Computer Acronyms(common) |
| UHP | Ultra High Purity | - | Computer Acronyms(common) |
| UHPLC | Ultrahigh-pressure Liquid Chromatography | - | Computer Acronyms(common) |
| UHT | Ultra High Temperature | - | Computer Acronyms(common) |
| UHTS | Ultra High-throughput Screening | - | Computer Acronyms(common) |
| UHV | Ultra High Vacuum | - | Computer Acronyms(common) |
| UHVEM | Ultra High Voltage Electron Microscopy | - | Computer Acronyms(common) |
| UIC | Underground Injection Control | - | Computer Acronyms(common) |
| UIHRS | Upflow Inclined High-rate Settlers | - | Computer Acronyms(common) |
| UJT | Unijunction Transistor | - | Computer Acronyms(common) |
| UKAEA | United Kingdom Atomic Energy Authority | - | Computer Acronyms(common) |
| UKAS | United Kingdom Accreditation Service | - | Computer Acronyms(common) |
| UKAWRG | United Kingdom Acid Waters Review Group | - | Computer Acronyms(common) |
| UKB | Unrestricted Kinetic Balance (in Calcns. Of Wave Functions And Energies) | - | Computer Acronyms(common) |
| UKIRT | United Kingdom Infrared Telescope | - | Computer Acronyms(common) |
| UKMO | United Kingdom Meteorological Office | - | Computer Acronyms(common) |
| ULDPE | Ultra Low Density Polyethylene | - | Computer Acronyms(common) |
| ULEV | Ultra Low Emission Vehicle | - | Computer Acronyms(common) |
| ULF | Ultra Low Frequency | - | Computer Acronyms(common) |
| ULFM | Unified Ligand Field Model (for Mol. Electronic Energies) | - | Computer Acronyms(common) |
| ULIRG | Ultraluminous Infrared Galaxy | - | Computer Acronyms(common) |
| ULPA | Ultra Low Penetration Air | - | Computer Acronyms(common) |
| ULSI | Ultra-large-scale Integration | - | Computer Acronyms(common) |
| ULTRA | Underground Leak Transport Assessment Model | - | Computer Acronyms(common) |