In Iyengar Yoga the twisting action of the spine is called lateral (from the sides) extension.  In sanskrit lateral extensions are called parivrtta sthiti; parivrtta meaning rotation, sthiti meaning state or being.  Lateral extensions are often referred to as seated twists.  Seated twists are wonderful for releaving back aches, they also aid in improving digestion and elimination.  Seated twists can be done easily using props such as chairs, bolsters and blankets. And range to quite challenging poses requiring balance and flexibility.