Threefold repetition

In chess and some other abstract strategy games, the threefold repetition rule (also known as repetition of position) states that a player can claim a draw if the same position occurs three times, or will occur after their next move, with the same player to move. The repeated positions do not need to occur in succession. The idea behind the rule is that if the position occurs three times, no progress is being made.

In chess, in order for a position to be considered the same, each player must have the same set of legal moves each time, including the possible rights to castle and capture en passant. Positions are considered the same if the same type of piece is on a given square. So, for instance, if a player has two knights and the knights are on the same squares, it does not matter if the positions of the two knights have been exchanged. The game is not automatically drawn if a position occurs for the third time – one of the players, on their move turn, must claim the draw with the arbiter.

In shogi, a fourfold repetition (千日手 sennichite) is required to end in a draw. Each player must have the same pieces in hand as well as the same position on the board. The result is a draw.

The relevant rule in the FIDE laws of chess is 9.2, which reads:

While the rule does not require that the position occur three times on nearly consecutive moves, it happens this way very often in practice, typically with one of the kings being put into perpetual check. The intermediate positions and moves do not matter – they can be the same or different. The rule applies to positions, not moves.

If the claim for a draw is incorrect, the opponent is awarded an extra two minutes and the game continues. Unreasonable claims may be penalized pursuant to article 12.6 which forbids distracting or annoying the opponent. Even if the claim is incorrect, any draw claim is also a draw offer that the opponent may accept.

...
Wikipedia