Yoga is a physical, mental, and spiritual practice or discipline, that aims to transform body and mind. The term denotes a variety of schools, practices and goals in Hinduism, Buddhism and Jainism, the best-known being Hatha yoga and Raja yoga. The term yoga is derived from the literal meaning of "yoking together" a span of horses or oxen, but came to be applied to the "yoking" of mind and body. The origins of Yoga have been speculated to date back to pre-vedic Indian traditions, but most likely developed around the sixth and fifth centuries BCE, in the same ascetic circles as the early sramana movements. The earliest accounts of yoga-practices are in the Buddhist Nikayas. Parallel developments were recorded around 400 CE in the Yoga Sutras of Patanjali, which combines pre–philosophical speculations and diverse ascetic practices of the first millennium BCE with Samkhya-philosophy. Hatha yoga emerged from tantra by the turn of the first millennium. Yoga gurus from India later introduced yoga to the west, following the success of Swami Vivekananda in the late 19th and early 20th century. In the 1980s, yoga became popular as a system of physical exercise across the Western world.