I heard the term "UMS" used to refer to a starcraft II custom map, and after looking it up it seems to refer to "Use Map Settings". What is the origin and history of this term?
The source is the original StarCraft, where the game mode for these custom maps was called "Use Map Settings":
(image from here)
It means the gameplay rules should be derived from the data in the map itself, instead of the regular StarCraft gameplay rules.