The John Nash Equilibrium is a concept in game theory, named after mathematician John Nash. It describes a situation in a strategic game where no player can benefit by changing their strategy while the other players keep theirs unchanged. In other words, each player's strategy is optimal given the strategies of all other players. This equilibrium helps to analyze competitive situations in economics, politics, and social sciences. It illustrates how individuals or groups make decisions that lead to stable outcomes, where everyone is making the best choice they can, considering the choices of others.