Ashtanga Yoga is named after the eight limbs of yoga mentioned in the Yoga Sutras of Patanjali.
Usually an Ashtanga practice begins with five repetitions of Surya Namaskara A and five repetitions of Surya Namaskara B, followed by a standing sequence. Following this the practitioner begins one of six series, followed by what is called the closing sequence. The six series are:
The Primary series: Yoga Chikitsa, Yoga for Health or Yoga Therapy
The Intermediate series: Nadi Shodhana, The Nerve Purifier (also called the Second series)
The Advanced series: Sthira Bhaga, Centering of Strength