What are muggins in cribbage and how do they affect the scoring in the game?

In cribbage, muggins is when a player fails to score points for combinations in their hand or during play, but their opponent notices and scores those points instead. This can happen if a player forgets to count certain combinations or fails to claim points during the game. Muggins can affect the scoring by allowing the opponent to gain points that the player missed, potentially changing the outcome of the game.