Game Theory is a division of Economics
Game theory is the study of economic decision-making. It is closer to the study of strategy than probability. Game theory uses hypothetical situations, games, to understand how decisions are made. The most commonly known game is the Prisoner's Dilema.
In the Prisoner's Dilema, two criminals are being interrogated in seperate rooms. If each keeps their mouth shut and admits nothing, they will each get ten days in prison. If one confesses and turns state's evidence, he will get off free and the other will get the death penalty. If they both confess, they will each get life in prison.
They both have the incentive to confess because regardless of whether the other confesses or not, their own situation will be better if they confess. Since they are unable to communicate and collude, they both confess. The outcome is that they both choose the sub-optimal outcome because it benefits them.