All yoga styles fall under the same blanket term of yoga, but in terms of their energy, they can be divided into two categories: Yang forms of yoga are active, whereas Yin forms are more passive. Yin yoga is meant to compliment active yoga styles like Slow Flow and Vinyasa.
Poses are held for longer periods of time to work on the deeper components of the physical body: connective tissue, ligaments, tendons, fascia, and even the bones. The long holds also foster an inner stillness that lends itself to a meditative practice. In a Yin practice, poses can be held from 3 minutes up to 20 minutes depending on where you are in your yoga practice.
Yoga props (bolster, pillow, blocks, blankets) are recommended tools for the practice.