What is "fifty-move rule"

n. (context chess English) The rule which states that a player can claim a draw after fifty consecutive moves by each side without a capture or a pawn move.

The fifty-move rule in chess states that a player can claim a draw if no capture has been made and no pawn has been moved in the last fifty moves (for this purpose a "move" consists of a player completing his turn followed by his opponent completing his turn). The purpose of this rule is to prevent a player with no chance of winning from obstinately continuing to play indefinitely , or seeking to win purely by tiring the opponent out.

All of the basic checkmates can be accomplished in well under 50 moves. However in the 20th century it was discovered that certain endgame positions are winnable but require more than 50 moves (without a capture or a pawn move). The rule was therefore changed to allow certain exceptions in which 100 moves were allowed with particular material combinations. However, more and more such winnable positions were later discovered, and in 1992 FIDE abolished all such exceptions and reinstated the strict 50-move rule.