U.V. 6, also simply known as Planet UV, is an icy planet in the UV star system. Uninhabited by humans and/or other humanoids, virtually in the middle of nowhere.
The extremely harsh environment (ranging from tundra-like to sub-polar, much like Earth's natural Poles) is life-sustaining to very few species of wildlife, and most are predatory. The planet is indicated by Toombs to be called "UV-6" as more of a joke, " 'cause even the sun can barely stand the weather ".
Riddick made his home on this world for roughly 5 years. Riddick chose to hide on this in order to protect Jack from being hunted as his accomplice; until he was found by Toombs and his crew of Mercs. Toombs was the known only survivor of the encounter, Riddick left U.V. 6 with Toombs' ship.