Full contact karate is a term used to differentiate between schools that spar full contact and those that use light contact point sparring.
It has many different derivatives but two main fundamental styles. One is similar to other competition karate where targets are specified and a clear strike to that target gains a fighter a full or half point. The blows are delivered with full contact, although heavy padding is often worn and in some cases body armour is also worn. The fight is stopped while points are awarded.
The other major style of full-contact karate is known as knockdown karate. This style of fighting was pioneered by the Kyokushinkai, founded by Masutatsu Oyama. In fighting the competitors have no or minimal shin padding and no body protection other than groin guards. Punches to the face and groin and joint attacks are prohibited but all bare-knuckle and elbow strikes to the body, and kicks (including kicks with the knee) against thigh, body, head and face are permitted, as are sweeps. A score is only made by knocking your opponent to the floor, or incapacitating them, or by sweep and controlled follow-up for half a point.
Most other karate styles that originated in Kyokushin, such as World Oyama Karate, Ashihara Karate, Enshin Karate, Seidō juku, Shidōkan, Shidōkan and Seidokaikan (the style that originated the K-1 kickboxing tournament) are also knockdown styles and use slight variations of the competition rules. A few other styles such as Kansuiryu Karate are also knockdown styles, but originated independently of Kyokushin.