Yin is the opposite of yang. Yang, in this case, referring to muscular activity, whether it be other types of yoga, biking, running, hiking, tennis etc. All these types of movement promote the building and strengthening of the musculature around the body.
Yin, on the other hand, does not involve any muscular effort. It is a practice which works towards increasing the flexibility and decreasing the thickness of the facia enveloping the body, especially surrounding the joints of the hips, spine, ankles and feet. This practice safeguards and in some cases, increases your room to move, allowing more freedom of movement, greater range of motion, more oil in the joints, improved posture and protection from injury.
Come out and try a class and make an investment towards your future of staying vibrant, flexible, injury and pain free throughout your future years.