According to Wikipedia:
"A split is a physical position in which the legs are in line with each other and extended in opposite directions. Splits are performed in various athletic activities, including dance, figure skating, gymnastics, martial arts, contortionism, synchronized swimming, cheerleading and yoga. A person who has assumed a split position is said to be "in a split."[1]
"When executing a split, the lines defined by the inner thighs of the legs form an unusually large angle of approximately 180 degrees. This large angle significantly stretches, and thus demonstrates excellent flexibility of, the hamstring and iliopsoas muscles. Consequently, splits are often used as a stretching exercise to warm up and enhance the flexibility of leg muscles."