Understanding Sanatana Dharma Part 5
(18) Astanga Yoga of Patanjali
Yoga is not merely a series of stretching exercises. It is a complete darsanam, or philosophy, born out of the mind of Patañjali. As such, it has its own specific ideas regarding the nature of jìva [the individual soul], jagat [the universe], ìsvara [God], samsara [bondage], moksha [liberation from bondage], and sàdhana [the means to attaining liberation from bondage].
Today, as a complete philosophy, the Yoga Darsanam is not widely followed. However with millions of people throughout the world becoming more and more interested in hatha-yoga àsanas and meditation, Patañjali’s system for personality refinement outlined as part of the philosophy is thriving indeed. This system is known astanga yoga. Not only is the astanga-yoga system practiced to some degree or the other by millions of hatha-yoga practitioners and meditators worldwide, but it has also been accepted as a tried-and-true system for personality refinement by other Indian darsanams that are more widely followed today, such as Advaita Vedànta.
an article on astanga yoga is available here