From the Yoga Yajnavalkya

"Yoga is said to be the union of the individual self and the supreme self (divine)... These are the limbs: yama, niyama, asana, pranayama, pratyahara, dharana, dhyana, and samadhi. Yama and niyama are subdivided into ten types. Eight asanas are important and among them, three are the most important. Dharana is said to be of five types. Dhyana is of six types; among them, three are said to be more important. Samadhi is one, but some think it to be of many divisions."

From the Yoga Yajnavalkya.