An acca is a group of individual bets brought together in one mega wager. Each leg of your acca, or accumulator, must win in order for you to win the overall bet and get a payout.

Similar to a straight forecast, a 'Reversed Forecast' consists of two selections, which you believe will finish in first and second, but it does not matter in which order they finish in, just as long as the two selections occupy the first two places.