Game Master, the term what defines who will run the game, atmosphere, scenes and non-player characters in game. I think Game Master or GM is the common term for that person around the gaming table involving the rpg session. Still, many games use their own terms to determine the "leader" of the game.
I was wondering, does people usually use the term "game master" involving all games regardless what game suggest the term for gm in that particular game is, or does Dungeon & Dragons players use Dungeon Master also in other games, as they are used to that term?
As I said Game Master is the common term for that particular player, but there is also similar terms used, like in D&D Dungeon Master and some funny adaptations in game's mood, like All Flesh Must Be Eaten's Zombie Master what suits the game well. White Wolf's World of Darkness game line uses term "storyteller", as game's are so called "storytelling" games where mood, characters and story are focused over killing and looting. I like that term the most and prefer to use it in most games I play.
A bit harder term is found in Call of Cthulhu, where Game Master is "keeper". Keeper is quite clever but I am not sure is it wildly used or functional enough term.
In the end it doesn't matter are you Game Master, Dungeon Master, Zombie Master, Storyteller or Keeper, in every games regardless of term your role in game is similar. Still I would say, when talking about rpg's generally the term "Game Master" or GM is well known, so it is used the most.