what is 50 move rule in chess

The 50-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 their turn. The rule exists to prevent a player with no chance of winning from obstinately playing on indefinitely in a position that cannot be won. The rule has a long history, and it was introduced into chess by Ruy López in his 1561 book. 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, winnable positions that required even more moves were later discovered, and in 1992, FIDE abolished all such exceptions and reinstated the strict 50-move rule over the board. In correspondence chess under ICCF rules, the fifty-move rule only applies when more than seven pieces remain on the board; when seven pieces or fewer remain, a win or draw may be claimed with reference to endgame tablebases.