U interface
UAV
UDP
Ultramafic
Ultramafic rock
Ultrasound
Ultraviolet
Unavailability
Unbalanced
Unbundling
Uncertainty
Unconfined aquifer
Underflow
Unsaturated
Updraft
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
Utility program
UTM
UV