The Yoga Sutras of Patanjali (2nd century BCE) is a foundational text of Yoga. In Indian philosophy, Yoga is the name of one of the six orthodox philosophical schools. Though brief, the Yoga Sutras are an enormously influential work on yoga philosophy and practice.
Patanjali divided his Yoga Sutras into 4 chapters or books (Sanskrit pada), containing in all 196 aphorisms, divided as follows:
1. Samadhi Pada - Concentration or Absorption (51 sutras)
2. Sadhana Pada - Practice or means to attain it (55 sutras)
3. Vibhuti Pada - Powers or Manifestations (56 sutras)
4. Kaivalya Pada - Isolation or Liberation (34 sutras)
Patanjali's Yoga is also called "ashtanga yoga" because of the eight "limbs" or steps of this Yoga prescribed in the second pada of the Yoga Sutras viz. Yama, Niyama, Asana, Pranayama, Pratyahara, Dharana, Dhyana and Samadhi.