Ashtanga Yoga
Ashtanga yoga as translated by Patanjali in the Yoga Sutras means "eight-limbed yoga". The Sage declared that there was a path of eight spiritual practices of internal purification that were necessary to reveal the Universal Self - these being:The function of Dharana, Dhyana, Samadhi and Pratyahara is to bring the mind under control so that, when this has been achieved and a state of purification has been obtained, the Six Poisons which surround the spiritual heart will eventually disappear. These Six Poisons are named: When these Six Poisons are eventually removed, the Universal Self is revealed. The concept of Ashtanga Yoga is that, when applied properly under the direct supervision of an experienced Ashtanga Guru, the disciplined mind, unfettered by both internal and external distractions, will lead to the attainment of the eight-limbed yoga described by Patanjali.
That is the basic premise of Ashtanga Yoga.