Compound probability in the context of multiple number bets refers to the likelihood of various combinations of outcomes occurring in a game, such as roulette. It is calculated by multiplying the probabilities of each individual bet or event since these bets can be independent or dependent. This approach allows players to assess the overall chance of winning when placing multiple bets simultaneously. Understanding compound probability helps in determining potential returns and managing risks associated with betting on various outcomes, providing a clearer picture of the chances of success in a gambling scenario.