What "threefold repetition" means in chess

Threefold repetition is a rule where a player can claim a draw if the same position occurs three times during the game. This means that the same pieces are on the same squares and the same player is on move with the same possible moves. The three positions do not have to occur consecutively and the player must claim the draw before making the move that would create the third repetition. This rule is intended to prevent players from repeating the same moves and trying to run down the clock or force a win by exhausting their opponent.