The word "foul" has several meanings, depending on its context.
1) In a general sense, it can refer to something that is unpleasant or offensive in taste, smell, appearance or quality. For example, "This food tastes really foul."
2) It can also be used as an adjective to describe something that is unfair or dishonest. For instance, "That was a foul move on the player's part."
3) In sports terminology, it refers to a penalty committed by a player, such as pushing, tripping or striking another player. An example would be, "He received a foul for elbowing his opponent."
4) Finally, in some dialects of English, the word can also mean something is going to happen or has happened, regardless of whether it's good or bad. For instance, "Something foul will happen if we don't act soon" or "That was a foul thing to do."