Yoga is an ancient practice that dates back to 5000 BC.
Swami Sivananda says:
The word ‘Yoga’ comes from a Sanskrit root ‘Yuj’ which means ‘to join’. In its spiritual sense, it is the process by which the identity of the individual soul and the Supreme Soul is realized by the Yogi. The human soul is brought into conscious communion with the Divine Reality. Just as camphor melts and becomes one with fire; just as a drop of water when it is thrown into the ocean, becomes one with the ocean; the individual soul, when it is purified, when it is freed from lust, greed, hatred and egoism, when it becomes pure (Sattvic), becomes one with the Supreme Soul. The science that teaches the way of acquiring this occult knowledge is called ‘Yoga Sastra’.
The word Yoga is also applicable in a secondary sense to all those factors and practices that are conducive to the final achievement or fulfillment of Yoga, and as such indirectly lead to final freedom or perfection. Similarly, though the one who has reached the final Asamprajnata Samadhi or union with Reality is called a Yogi, one who is attempting to get perfection in Yoga is also called a Yogi.
Yoga philosophy is one of the six systems of Hindu philosophy. Unlike so many other philosophies of the world, it is a philosophy that is wholly practical. Yoga is an exact science based on certain immutable Laws of Nature. It is well known to people of all countries of the world interested in the study of East civilization and culture, and is held in awe and reverence as it contains in it the master-key to unlock the realms of Peace, Bliss, Mystery and Miracle. Even the philosophers of the West found solace and peace in this Divine Science. Jesus Christ himself was a Yogi of a superior order, a Raja-Yogi indeed. The founder of the Yoga Philosophy, Patanjali Maharishi, was not only a Philosopher and a Yogi, but a Physician as well. He is said to have lived about three hundred years before Jesus Christ.
Yoga is that state of Absolute Peace wherein there is neither imagination nor thought. Yoga is control of mind and its modifications. Yoga teaches us how to control the modifications of the mind and attain liberation. It teaches us how to transmute the unregenerate nature and attain the state of Divinity. It is the complete suppression of the tendency of the mind to transform itself into objects, thoughts, etc. Yoga kills all sorts of pain, misery and tribulation. It gives you freedom from the round of births and deaths, with its concomitant evils of disease, old age, etc., and bestows upon you all the Divine Powers and final liberation through super-intuitional knowledge.
Equanimity is Yoga. Serenity is Yoga. Skill in actions is Yoga. Anything by which the best and the highest in life can be attained is also Yoga. Yoga is thus all-embracing, all-inclusive and universal in its application leading to all-round development of body, mind and soul.
Yoga is primarily a way of life, not something which is divorced from life. Yoga is not forsaking of action, but is efficient performance in the right spirit. Yoga is not running away from home and human habitation, but a process of moulding one’s attitude to home and society with a new understanding. Yoga is not a turning away from life; it is spiritualization of life.