Room speed
From GMWiki, the Gamemaker Wiki.
room_speed is a built-in global variable. It should contain the FPS you would like your game to run at. Game Maker will limit the game from running more frames per second than this value. However, if the game has too many objects or particles, the actual FPS may drop below the room_speed, depending on the speed of the hardware it is running on, how the game is programmed, use of effects etc.

