Yin Yoga is a slow-paced style of yoga as exercise, incorporating principles of traditional Chinese medicine, with asanas (postures) that are held for longer periods of time than in other styles. For beginners, asanas may be held from 45 seconds to two minutes; more advanced practitioners may stay in one asana for five minutes or more. The sequences of postures are meant to stimulate the channels of the subtle body known as meridians in Chinese medicine and as nadis in Hatha yoga.
Yin Yoga poses apply moderate stress to the connective tissues of the body—the tendons, fasciae, and ligaments—with the aim of increasing circulation in the joints and improving flexibility. A more meditative approach to yoga, its goals are awareness of inner silence, and bringing to light a universal, interconnecting quality.
Source https://en.wikipedia.org/wiki/Yin_Yoga