The Back Handspring is performed with the legs together at all times.  The gymnast must start with arms overhead or in front, and jump backward while arching the back.  As the feet leave the ground, the back remains arched until the hands arrive on the ground.  The gymnast then shifts to a hollow position, and springs from the hands back to the feet, ending with arms in front.  This skill often leads to harder tumbling elements, including many flipping skills.  It is considered to be extremely important in the sport.