What is Game Theory?
Put simply, Game Theory is the analysis of Games.
A Game is a social interaction between two or more players, where the outcome of that interaction depends on the choices made by the players. Each player as a list of Strategies that they can choose from, and the chosen strategies determines the Outcome. Since the outcome depends on what all of the players choose, players need to think strategically: “what will the other player(s) do?” (Important because it motivates the assumption of common knowledge of rationality)
Game Theorists go deep on really simple, straightforward games (e.g. The Stag Hunt), not because the game is any fun to play, but because it represents a common feature of social interaction. These interactions include games and even parts of games (e.g. the auction phase in Fleet, the semi-cooperation in Dead of Winter, or the shared resources in Brass).