What exactly does it mean to have your cherries popped?

Broken hymen: This refers to the tearing open of the hymen, a membrane partially across the vaginal opening during the first act of intercourse (loss of virginity). Usually this causes bleeding if the hymen is intact. Sometimes some previous non-sexual act can break this open and occasionally it is not present and there is no bleeding. "popping" is the expression for the penetration of the hymen.