In a game where two players can either cooperate or defect, what is a Nash Equilibrium?

A Nash Equilibrium is a situation in a game where each player has chosen their best strategy, given the strategy chosen by the other player. This means that neither player can gain anything by changing their strategy while the other player keeps theirs the same. For example, in a game where two players can either cooperate to get a better outcome or defect for a quick gain, if both players decide to defect, they reach a Nash Equilibrium. In this case, if one player tries to switch to cooperating while the other continues to defect, the cooperator will end up worse off. Therefore, both players sticking to their choice of defecting is the most stable outcome.