UGC - User Generated Content
Uhura - She was the communications officer of the NCC-1701 Enterprise.
Undine - Also known as Species 8472. They are from a place known as Fluidic Space and can change their appearance to look like anyone.
uniform - An outfit worn by a group of people that is always standard.
unimatrix - A subdivision used by the Borg to designate regions of space or groups of Borg.
union - To join together
Universal - Point Defense System - A turret which automatically targets nearby enemies especially small threats such as mines or fighters.
universe - all existing matter and space considered as a whole
USS - United Star Ship
USS Defiant - A name given to a few ships in Starfleet. The most famous is probably the USS Defiant that was stationed at Deep Space 9. It played an important role in the Dominion War. It was originally developed in response to the Borg threat.