Yin Yoga:

The class is designed to calm, rather than energize. Poses are held for 3-5 minutes, allowing the nervous system to relax, heal and repair the body. This style focuses on stretching the deepest layers of the physical body, the connective tissues, ligaments, tendons, bones, and joints. Most poses are done either seated or lying down and props are available to support your body. Yin cultivates patience, flexibility, endurance, contentment, and letting go.

Recommended for:

All levels. 
Especially for: people who want to balance their active/demanding lifestyles with a calming, relaxing practice; people who are looking to open up tight areas of their body (hips, thighs, back, etc) to allow for a better range of motion and ease of movement in day to day life.