In hockey, PIM stands for penalty in minutes. Penalties are given to players who break the official rules of the game. They are typically enforced by detaining the player in the penalty box for a specific number of minutes.
During a player’s penalty, he is not allowed to participate in the game. Penalties are called by the referee and sometimes by the linesmen. In some cases, the team does not replace the player during the penalty, leaving them short-handed. During this time, the other team has one more player than the short-handed team and is said to be on a "power play." When the penalty expires, the player can return to the game.