Yoga is a group of physical, mental, and spiritual practices or disciplines which originated in ancient India. Yoga is one of the six orthodox schools of Hindu philosophical traditions. There is a broad variety of yoga schools, practices, and goals in Hinduism, Buddhism, and Jainism. Among the best-known types of yoga are Hatha yoga and Raja yoga.

The origins of yoga have been speculated to date back to pre-Vedic Indian traditions; it is mentioned in the Rigveda,  but most likely developed around the sixth and fifth centuries BCE, in ancient India's ascetic and srama?a movements. The chronology of earliest texts describing yoga-practices is unclear, varyingly credited to Upanishads. The Yoga Sutras of Patanjali date from the first half of the 1st millennium CE, but only gained prominence in the West in the 20th century. Hatha yoga texts emerged around the 11th century with origins in tantra.

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. Yoga in Indian traditions, however, is more than physical exercise; it has a meditative and spiritual core. One of the six major orthodox schools of Hinduism is also called Yoga, which has its own epistemology and metaphysics, and is closely related to Hindu Samkhya philosophy. 

Hinduism

Classical yoga

Yoga is considered as a philosophical school in Hinduism. Yoga, in this context, is one of the six astika schools of Hinduism (those which accept the Vedas as source of knowledge).

Due to the influence of Vivekananda, the Yoga Sutras of Patanjali have since the 20th century been considered the foundational scripture of classical yoga.Before then, other works such as the Bhagavad Gita and the Yoga Vasistha were considered the most central, while Tantric Yoga and Hatha Yoga prevailed over Ashtanga Yoga.

Many studies have tried to determine the effectiveness of yoga as a complementary intervention for cancer, schizophrenia, asthma, and heart disease. The results of these studies have been mixed and inconclusive. On December 1, 2016, yoga was listed by UNESCO as an intangible cultural heritage.

Ashtanga yoga

Main articles: Yoga Sutras of Patanjali and Raja yoga

Swami Vivekananda equated raja yoga with the Yoga Sutras of Patanjali.

Yoga as described in the Yoga Sutras of Patanjali refers to Ashtanga yoga. The Yoga Sutras of Patanjali is considered as a central text of the Yoga school of Hindu philosophy, It is often called "Raja yoga", "yoga of the kings," a term which originally referred to the ultimate, royal goal of yoga, which is usually samadhi, but was popularised by Vivekananda as the common name for Ashtanga Yoga.

Ashtanga yoga incorporates epistemology, metaphysics, ethical practices, systematic exercises and self-development techniques for body, mind and spirit. Its epistemology (pramanas) is same as the Samkhya school. Both accept three reliable means to knowledge – perception (pratyak?a, direct sensory observations), inference (anumana) and testimony of trustworthy experts (sabda, agama). Both these orthodox schools are also strongly dualistic. Unlike the Sa?khya school of Hinduism, which pursues a non-theistic/atheistic rationalist approach, the Yoga school of Hinduism accepts the concept of a "personal, yet essentially inactive, deity" or "personal god". Along with its epistemology and metaphysical foundations, the Yoga school of Hindu philosophy incorporates ethical precepts (yamas and niyamas) and an introspective way of life focused on perfecting one's self physically, mentally and spiritually, with the ultimate goal being kaivalya (liberated, unified, content state of existence).

 Hatha yoga

Main article: Hatha yoga

A sculpture of Gorakshanath, a celebrated 11th century yogi of Nath tradition and a major proponent of Hatha yoga.

Hatha yoga, also called hatha vidya, is a kind of yoga focusing on physical and mental strength building exercises and postures described primarily in three texts of Hinduism:

Hatha Yoga Pradipika, Svatmarama (15th century)

Shiva Samhita, author unknown (1500[59] or late 17th century)

Gheranda Samhita by Gheranda (late 17th century)

Many scholars also include the Goraksha Samhita by Gorakshanath of the 11th century in the above list. Gorakshanath is widely considered to have been responsible for popularizing hatha yoga as we know it today.

Vajrayana Buddhism, founded by the Indian Mahasiddhas, has a series of asanas and pranayamas, such as tummo (Sanskrit ca??ali) and trul khor which parallel hatha yoga.

Reference Links:  https://en.wikipedia.org/wiki/Yoga