Nim is a mathematical game of strategy played between two players. The game involves a number of piles of objects, such as stones or coins. Players take turns removing any number of objects from a single pile. The player who takes the last object wins the game. The game can be played with different rules, such as varying the number of objects in each pile or allowing players to take only one object at a time. Nim has been studied in combinatorial game theory, leading to strategies that can guarantee a win for the first player under optimal play conditions.