Twist 1 is the name of this exercise. It is performed in the Classical Mat Repertoire. Your goal is to twist from your waist, wringing it out like a rag.
Perform the 3 additional mat exercises – Side Twist, Saw and Scissors from the Stomach Series to warm your waist and stretch your hamstrings and then do Twist 1.
This is a great series to whittle your waist and tighten your stomach muscles.