YOGA - An introduction:

Yoga conventionally means to "unite" or "join" the various aspects of our personality which were never really divided in the first place. It also means to "yoke" or to engage ourselves in a self-training program. Yoga means, working with each of the levels or aspects of our being individually, and then unifying all of those into their original whole, or Yoga. Yoga is a Sanskrit word coming from the root "yuj" and relates to both the processes or practices referred to as Yoga and also the goal itself, which is also called Yoga. As the goal, the word Yoga means Samadhi, the deep, transcendent realization of the highest truth (as per the commentary on the Yoga sutras of Patanjali, by Vyasa).
Despite many misconceptions, Yoga is a meta-psychological process, not a religion or a system of physical fitness per se. Yoga is an ancient system of personal discipline that integrates physical, psychological, and spiritual practices. However, Yoga practices can be integrated into religious observance and can deepen the religious experience of devotees of any religion. The word Yoga is synonymous with Samadhi, the transcendent, superconscious state of being or God realization, referred to by Jesus as “the peace that passeth all understanding.”
Philosophically, Yoga presents a hypothesis that this transcendent level of consciousness is available to humans and offers a comprehensive base of theory, ethical interaction, and, most important, technique to help us access it. For the most part Yoga is a practical, not speculative, philosphy. The Yoga-Sūtra of Patanjali is the primary textbook, or technical manual, for the field. The definition of the word Yoga depends on the context of usage, and, in English, may refer to four possible meanings:
1. A state of transcendent consciousness—samādhi
2. One of the six branches of formal Indian orthodox philosophy that present pathways to this consciousness
3. An ancient system of spiritual disciplines and practices that are said to lead to this state of consciousness
4. A tradition, or school, of Yoga, that perpetuates those practices
Most popular works on Yoga in English maintain that the term Yoga emerges from the Sanskrit root yuj. They generally select as their definition: “union; to join, restrain, keep under control, as in yoking.” Their contention is that while this is correct in itself, it does not reflect the primary focus of Yoga’s core texts, including the Yoga-Sūtra of Patanjali. Vyāsa, in his commentary on the Yoga-Sūtra, asserts, “Yoga is samādhi.” At its etymological core, and particularly in the context of the Yoga-Sūtra, the word Yoga is a technical term that refers primarily to a transcendent state of consciousness—samādhi—and secondarily to the practices that facilitate this awareness. However, Yoga is something that cannot be defined, because to define is to confine. And Yoga is a way of life. Yoga is life. And Yoga is beyond life. And as the meaning of anything is the experience that it gives, so is it with Yoga.