Collateral estoppel, known in moern terminology as issue preclusion, is a common law estoppel doctrine that prevents a person from relitigating an issue. Simply put, "once a court has decided an issue of fact or law necessary to its judgment, that decision ... preclude[s] relitigation of the issue in a suit on a different cause of action involving a party to the first case." This is for the prevention of legal harassment and to prevent the abuse of legal resources.