A Four-Fold Accumulator is one bet made up of four selections in different events. If they all win, so do you. But if any of the selections lose, your bet does too.
If a bet is on the winner of a game, that is called a moneyline bet. If you're betting that a team will win or lose by a certain amount of points, that is called a spread bet. If you combine multiple outcomes into one bet, that is called a parlay.