1. To come apart in pieces. The house is so old that the plaster on this wall has busted up—there are bits of it all over the floor.

2. To end a partnership of some kind, often a romantic relationship. I'm so sad to hear that Mara and John busted up—I thought those two would be together forever. The Beatles busting up is considered a pivotal moment in rock history.

3. To induce the end of a partnership of some kind, often a romantic relationship. I heard that constant dishonesty busted up their marriage.

4. To physically attack someone, as with punches and other blows, such that they suffer significant injury. In this usage, a noun or pronoun can be used between "bust" and "up." The captain of the football team swore he would bust me up if I ever talked to his girlfriend again. I can't believe that skinny kid busted up the school bully!