U interface
UAV
UDP
Ultramafic
Ultramafic rock
Ultrasound
Ultraviolet
Ulu
Umacha
Unavailability
Unbalanced
Unbundling
Uncertainty
Unconfined aquifer
Unconfined ground water
Unconformity
Underflow
Underground feeder
Underground service entrance
Understory
Undescribed
Ungulates
Unimodal
Uninterruptible power supply
Unsaturated
Unsaturated zone
Updraft
Upland
Upland community
Uplifting
Uplink
Upslope flow
Upstream
UPT
Uptime
Uracil
Uranium
Urea
Uremia
Ureter
Urethra
Urine
Urologist
Urology
Urticaria
USAID
USDA
User
User datagram protocol
User information
User interface
USGS
USNO
Usury
UTC
Uterus
Utility interactive inverter
Utility program
UTM
UV