Yoga is a philosophy and set of practices that originated in Ancient India. There are mulitple yoga schools and traditions which are sometimes very different from one another. Some are very austere and advocate ascetic practices, others encourage practitioners to celebrate life in all its forms. Today, yoga in the West is mostly associated with the physical practice of yoga poses; it has taken on many different forms and is practiced in ashrams as well as in gyms.
Yoga's current popularity, regardless of the approach or tradition, is most likely due to its mental and physical benefits. Yoga practice teaches optimal physical alignment while providing the tools to quiet the mind. Yoga is accessible to all, children, people with disabilities, athletes, senior citizens, and can be practiced in educational, athletic, private, or corporate environments.