In a non-cooperative game represented by a payoff matrix, if both players choose their strategies such that neither can gain a higher payoff by unilaterally changing their strategy, what is this situation called?

In game theory, when both players in a non-cooperative game choose their strategies in a way that neither can improve their payoff by changing their own strategy alone, this situation is called a Nash Equilibrium. It means that each player's decision is optimal given the choice of the other player. For example, imagine two friends deciding whether to go to a movie or a concert. If they both choose the movie and neither would enjoy changing to the concert alone, they are in a Nash Equilibrium because neither can do better by switching. This concept helps us understand how individuals make decisions in competitive situations where their outcomes depend on the choices of others.