Boxing (or pugilism) is a combat sport of prehistoric origin in which two participants of similar weight fight each other with their fists in a series of one to three-minute intervals called rounds. Victory is achieved if the opponent is knocked down and unable to get up before the referee counts to ten (a Knockout, or KO) or if the opponent is deemed too injured to continue (a Technical Knockout, or TKO). If there is no stoppage of the fight before an agreed number of rounds, a winner is determined either by the referee's decision or by judges' scorecards. In some countries with their own fighting sports, the sport is referred to as "English Boxing" (e.g. in France to contrast with French Boxing).