K.O. is a term most commonly used in boxing and martial arts that stands for "knockout." However, there are a variety of synonyms that can be used in its place. One such synonym is "TKO," which stands for "technical knockout," indicating that a fighter was unable to continue due to a technical issue rather than being knocked out cold. Other synonyms include "KO'd," "disqualified," "stopped," or "overwhelmed." In everyday usage, "out cold," "unconscious," or "totally knocked out" may also be used in place of K.O. Regardless of the term used, they all convey the same meaning of a fighter ending a bout due to being incapacitated in some form.