Although the term yin yoga is relatively modern, the style has roots in Daoism and Daoist yoga that was practiced in China and Taiwan thousands of years ago.
The practice consists of a series of passive floor poses that are practiced in a static way, (i.e., there is little to no ‘flow’ element to a yin yoga class). Most of the poses are held for an extended length of time, between three and ten minutes. During a yin yoga class, you do less poses, but you hold them for much longer.
Yin yoga mainly works the lower body, specifically the hips, thighs, glutes, and lower back. Most people have a lot of tension and inflexibility in these areas and find that regular practice of yin yoga helps to release this tightness.