A technical knock-out (TKO) is a special term used in boxing, considered by the judges, when one boxer seems too wounded to continue.
In the Punch-Out!! games when a boxer forfeits the match after being knocked down a certain numbers of times. In the NES, SNES, and Wii editions of Punch-Out!!, a TKO occurs after a boxer is knocked down three times within a single round. There are some opponents who can only be beaten by TKO.
In Punch-Out!! for the Wii, Hitting the - button on your wii remote can save Mac from going down (TKO's only.) and losing the match. Instead, he will almost go down, then suddenly put his foot down and raise his head angrily, then the fight will continue with you regaining half your health. (Note: You must hit the - button at the right time, otherwise Mac will fall down and lose to TKO)