Ippon (一本, lit. "one full point") is the highest score a fighter can achieve in a Japanese martial arts ippon-wazari contest, usually kendo, judo, karate or jujutsu.
In karate
In shobu ippon kumite, a method of karate competition, an ippon is awarded for a technique which is judged as decisive, this is usually a move which connects cleanly, with good form and with little opportunity for the opponent to defend against it. Kicks to the head of an opponent or judo throws followed up with a strike to the downed opponent are particularly likely to be considered a winning ippon technique. A competitor is declared the winner upon achieving a judgment of ippon.
Occasionally shobu nihon kumite is used, in which two decisive strikes (or four less-decisive strikes, scored as waza-ari) are required for a win. In many tournaments, sanbon scoring is used. This promotes a flashier style of fighting more suited to a spectator sport. More traditional tournaments usually use ippon scoring.