What is yoga?

Yoga  is a commonly known generic term for physical, mental, and spiritual disciplines which originated in ancient India.Specifically, yoga is one of the six āstika ("orthodox") schools of Hindu philosophy. One of the most detailed and thorough expositions on the subject are the Yoga Sūtras of Patañjali. Various traditions of yoga are found in Hinduism, Buddhism, Jainism and Sikhism.
Pre–philosophical speculations and diverse ascetic practices of first millennium BCE were systematized into a formal philosophy in early centuries CE by the Yoga Sutras of Patanjali.By the turn of the first millennium, Hatha yoga emerged as a prominent tradition of yoga distinct from the Patanjali's Yoga Sutras. While the Yoga Sutras focus on discipline of the mind, Hatha yoga concentrates on health and purity of the body.
Hindu monks, beginning with Swami Vivekananda, brought yoga to the West in the late 19th century. In the 1980s, yoga became popular as a physical system of health exercises across the Western world. Many studies have tried to determine the effectiveness of yoga as a complementary intervention for cancer, schizophrenia, asthma and heart patients. In a national survey, long-term yoga practitioners in the United States reported musculo–skeletal and mental health improvements.