From the White Wolf Wiki, the most complete White Wolf reference

In tabletop role-playing games, one player becomes a narrator, referee, judge and final arbiter of the rules governing adventures and their effect on the advancement of other players' characters. Depending on the game system, this particular individual could be called "Game Master", "Storyteller", "Director", "Narrator", "Administrator", or one of a host of other names. By far, Dungeon Master is the oldest of these, owing its existence back to the role-playing game's roots in Dungeons & Dragons, which popularized the term.