As the turn passes from player to player, if someone cannot make a move, they're going to do one of two things, based on the game being played. In "block" games (or if there are no tiles left inthe boneyard), a player must "pass" if he cannot make a move. In a "draw" game, a player can draw a tile from the boneyard. Depending on the game, he can then either play it (if it fits, and if the rules allow), pass (if he cannot play the drawn tile), or continue drawing until he can make a move or the boneyard is empty.