“Ashtanga” means verbatim eight branches. They are described by Patanjali as:

Yama (restraint)
Niyama (discipline)
Asana (positions)
Pranayama (breathing control)
Pratyahara (withdrawal of the senses)
Dharana (concentration)
Dhyana (meditation)
Samadhi (contemplation / deep meditation)
These branches carry one another. Asana training (positions) must be established for proper exercise of pranayama (breathing exercises) and is the key to the development of yamas(restraint) and niyamas(discipline). When these four externally oriented parts are firmly anchored, the last four internally oriented parts will eventually develop themselves.

Soul of Yoga