u (representing the greek mu) - micro
U Universe
UA United Artists
UAR United Arab Republic
UAR User Action Routine
UARS Upper Atmosphere Research Satellite (Espacial)
UART Universal Asynchronous Receiver Transmitter
UBA UniBus Adapter [DEC]
UBC Universal Bibliographic Control
UBC University of British Columbia
UBM Unpressurized Berthing Mechanism (Espacial)
UCAR University Corporation for Atmospheric Research
UCB University of California at Berkeley
UCD Uniform Call Distributor (Telefonia)
UCD University of California at Davis
UCI University of California at Irvine
UCL University College London
UCLA University of California at Los Angeles
UCR University of California at Riverside
UCSB University of California at Santa Barbara
UCSC University of California at Santa Cruz
UCSD University of California at San Diego
UCSF University of California at San Francisco
UDB Unified DataBase
UDMH Unsymmetrical DiMethyl Hydrazine (Espacial)
UDP User Datagram Protocol
UEC User Environment Component
UFO Unidentified Flying Object (Espacial)
UGC Uppsala General Catalog (Espacial)
UH Upper Half
UHF Ultra High Frequency (300-3000MHz)
UID Unique IDentifier
UID User IDentification [UNIX]
UIMS User Interface Management System
UIT Ultraviolet Imaging Telescope (Espacial)
UIUC University of Illinois at Urbana-Champaign
UK United Kingdom
UKST United Kingdom Schmidt Telescope (Espacial)
UL Underwriters Laboratory
ULANA Unified Local-Area Network Architecture
UMOC Ugliest Man On Campus [MIT]
UMT Universal Military Training
UN United Nations
UNESCO United Nations Educational, Scientific, & Cultural Organization
UNICEF United Nations International Children's Emergency Fund 
UNICS UNiplex Information Computer Services
UNIX System Operation
UNMA Unified Network Management Architecture [AT&T]
UNO United Nations Organization
UP Union Pacific (Rede ferroviária, nome de companhia)
UPC Universal Product Code
UPI United Press International
UPI United Press International (nome de companhia)
UPS Uninterruptible Power Supply
UPS United Parcel Service (nome de companhia)
UR University of Rochester
URI University of Rhode Island
US United States (da América)
USA Union of South Africa
USA United States Army
USA United States of America
USAF United States Air Force
USAFA United States Air Force Academy (em Colorado Springs)
USAN University Satellite Network
USB Upper Side Band
USC University of Southern California
USCG United States Coast Guard
USDA United States Department of Agriculture
USES United States Employment Service
USFL United States Football League
USGS United States Geological Survey
USIA United States Information Agency
USM United States Mail
USMC United States Marine Corps
USMP United States Microgravity Payload (Espacial)
USN United States Navy
USO United Service Organizations
USO Unix Software Operation
USP United States Pharmacopeia
USPS United States Postal Service
USR User Service Routines
USS United States Ship
USSR Union of Soviet Socialist Republics
USSS User Services and Systems Support
USW Und So Weiter
UT Universal Time (também conhecido como GMT, UTC ou Zulu Time)
UT University of Tennessee
UT University of Texas
UT UTah
UTC Coordinated Universal Time (também conhecido como UT)
UTC Universal Coordinated Time (também conhecido como UT)
UTnet University of Texas Network
UTP Unshielded Twisted Pair [Telecomunicações, Networking]
UUCP UNIX-to-UNIX Copy Program
UUG Unix User Group
UV UltraViolet
UVS UltraViolet Spectrometer
UW UnderWriter
UW Univ of Wisconsin
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