There are lots of references to Yoga in Hindu scriptures, especially in the Gita, the Upanishads and other Puranas. Here's a selection of quotations from Sanskrit literature, which try to define or qualify Yoga. The Bhagavad Gita: "Yoga is skill in actions." "Yoga is balance (samatva)" "Yoga is known as the disconnection (viyoga) of the connection (samyoga) with suffering." Yoga-Sutra: " Yoga is the control of the whirls of the mind." Yoga-Bhashya: " Yoga is ecstasy (samdhi)." Maitri-Upanishad: "Yoga is said to be the oneness of breath, mind, and senses, and the abandonment of all states of existence." Yoga-Yajnavalkya: "Yoga is the union of the individual psyche (jva-tman) with the transcendental Self (parama-tman)." Yoga-Bjam: " Yoga is the unification of the web of dualities (dvandva-jla)." Brahmand-Purana: " Yoga is said to be control." Rja-Mrtanda: " Yoga is the separation (viyoga) of the Self from the earthly (prakriti)." Yoga-Shikha-Upanishad: " Yoga is said to be the unity of exhalation and inhalation and of blood and semen, as well as the union of sun and moon and of the individual psyche with the transcendental Self." Katho-Upanishad: " This they consider Yoga: the steady holding of the senses."