The fifty-move rule is an official chess rule that allows a player to claim a draw if fifty consecutive moves have been played by each side without any pawn move or capture.
This rule exists to prevent games that are theoretically drawn — but where one player refuses to agree to a draw — from going on indefinitely. In practice, it comes into play in difficult endgames such as rook versus bishop endings, or when a defending player tries to hold an inferior position simply by running out the clock. The count resets to zero as soon as a pawn advances or any piece is captured.
In practice, if you are defending a position and your opponent cannot make progress, keep track of the move count — many digital clocks and online platforms display this counter automatically. Once fifty moves have passed without a pawn move or capture, you are entitled to claim a draw from the arbiter, or the software will apply the rule automatically.