Yoga is a Hindu spiritual and ascetic discipline, a part of which, including breath control, simple meditation, and the adoption of specific bodily postures, is widely practiced for health and relaxation.¹
Yoga (Sanskrit, योग yóga) originates from ancient India and the goal of the person practicing yoga, is the attainment of a state of perfect spiritual insight and tranquility while meditating on the Hindu concept of divinity or Brahman. The word yoga literally means “yoke”, from a root yuj meaning to join, to unite, or to attach. Someone who practices yoga or follows the yoga philosophy with a high level of commitment is called a yogi or yogini.
The yoga widely known in the West is based on hatha yoga, which forms one aspect of the ancient Hindu system of religious and ascetic observance and meditation, the highest form of which is raja yoga and the ultimate aim of which is spiritual purification and self-understanding leading to samadhi or union with the divine.²
There are many different styles of yoga. Below some are listed.
¹ New Oxford American Dictionary (digital version), 2012-02-13