This program uses Monte Carlo simulations as an AI for Tic Tac Toe. What exactly does that mean? It means that the AI uses the monte carlo method to probabilistically determine its best move. Without knowing any rules of the game, the AI runs through thousands of simulations of possible games each turn and after viewing the results, chooses the 'best/most likely to win' spot. This makes the AI appear to be 'smart' (i.e. have a good strategy) to the user, but in fact, it relies on no strategy at all.