Yoga, meaning 'yoke' in Sanskrit, is a family of ancient spiritual practices originating in India. It is one of the six schools of Hindu Philosophy, in which it is often paired with Samkhya, and they are referred together as the Samkhya-Yoga school. The diversity within Yoga philosophy itself is traditionally classified into four main braches: Karma Yoga (yoga of action), Jnana Yoga (yoga of knowledge), Bhakti Yoga (yoga of devotion), and Raja Yoga (yoga of meditation), but other classifications do exist. It remains a vibrant living tradition in which the common goal of all branches is liberation from suffering by attainment of enlightenment.
In the later half of the twentieth century, a co-movement of Yoga teachers to the West and travelers coming to India to study Yoga led to a great rise in teaching of Yoga in western countries. As with Yoga itself, these teachings are incredibly diverse but it can be said that outside India, Yoga has become primarily associated with the asanas (postures) of Hatha Yoga (a development within Raja Yoga placing more emphasis on physical practice than meditation). Indeed for many practitioners today, Yoga is a purely physical exercise (akin to aerobics and pilates), and is taught without the rest of its philosophy. According to a 2005 study, there are now over 16 million yoga practitioners in the USA alone. This figure suggests the worldwide total may be over 100 million.
Ancient Hindu texts establishing the basis for yoga include the Upanishads, the Bhagavad Gita, the Yoga Sutras of Patanjali, the Hatha Yoga Pradipika and many others, which specify the criteria of having successfully mastered a particular yoga technique.