A butterfly kick or horse kick (xuànzi, circle) is a kick featured within many disciplines of martial arts, but originally practiced in Chinese martial arts, in particular modern Wushu. It is so named because as the legs reach the apex of their arc the arms are stretched out, leaving all limbs extended in a position similar to that of a butterfly’s wings in-flight (however, note that the original Chinese word for this technique contains no references to butterflies or kicks).
Although the specific nature of the kick varies, it is generally composed of a twist of the body while both legs are lifted from the ground and swung around, while the torso remains as horizontal as possible. It is an advanced maneuver that requires the use of the whole body and the strike can occur with either leg. It is often seen as a kick used to “cut a swathe” through multiple opponents. However, in traditional Chinese longfist, it is used defensively to evade an opponent’s floor sweep and land on the enemy’s vulnerable side.
There are many variations, and different movements may be captured under the same name or likewise similar movements given under a different name depending on the martial arts school or style. It can be executed either from standing or from a step up run. Because of its aesthetic appeal the move is often used in movies (although more as a jump than a kick).
[From Wikipedia. Original page is here]