Game theory is a branch of mathematics that studies strategic interactions between rational decision-makers. It helps in understanding the behavior of individuals in strategic situations where the outcome of their actions depends on the choices of others.

Examples of Game Theory:
- The Prisoner's Dilemma
- The Battle of the Sexes
- The Chicken Game
- The Ultimatum Game
- The Stag Hunt

Nash Equilibrium:
Nash Equilibrium is a concept in game theory that describes a situation in which each player in a game is making the best decision possible, given the decisions of the other players. In other words, no player has an incentive to change their strategy unilaterally.

Explanation:
In a Nash Equilibrium, each player's strategy is optimal given the strategies of the other players. If any player were to change their strategy, they would not improve their payoff. This concept is named after John Nash, who introduced it in his doctoral thesis in 1950.
For example, in the Prisoner's Dilemma game, the Nash Equilibrium occurs when both prisoners choose to confess, even though both would be better off if they remained silent. If one prisoner were to change their strategy to remain silent, they would end up with a worse outcome.
In summary, Nash Equilibrium is a crucial concept in game theory that helps in predicting the behavior of rational decision-makers in strategic situations. It provides insight into how individuals will act when their decisions are interdependent.