A Nash equilibrium is a concept in game theory where no player can benefit by changing their strategy while the other players keep theirs unchanged. In simpler terms, it represents a situation where everyone involved has chosen a strategy, and no one has anything to gain by altering their choice. This means that each player's decision is optimal, given the decisions of others. In a Nash equilibrium, players are aware of the strategies of their opponents and make their choices accordingly. This concept is named after mathematician John Nash, who contributed significantly to the understanding of strategic interactions in competitive situations.