Yoga is a Sanskrit word meaning "union of Atman (individual Soul) with Brahman (Universal Soul)." "Atman" and "Brahman" are both Hindu theological terms.
Interestingly, the Sanskrit root for "yoga" is "yuj;" i.e., "to yoke" [to the Spirit], and the Latin root for "religion" is "religio;" i.e., "to link-back" [to the Spirit]. Therefore it is a fallacy that "yoga" is not "religion" as the two words basically have the same meaning. With this basic understanding, it sounds almost as odd to say "I do yoga" as it does to say "I do religion." Fine—but which one?
Of course, it is in the Hindu religion that one finds all the many forms of Yoga. The Hindu religion (also known by the names "Sanatan Dharma," "Vedic Dharma" and even "Yoga Dharma") is the spiritual foundation from which arose the Buddhist, Jain and Sikh Dharmas or religions.
For the Hindu, on the journey to Spiritual-Realization, the many Yoga/Hindu spiritual disciplines take into consideration all aspects of one's being. The classic Yogas are progressive in nature; i.e., Karma Yoga (ethics), Bhakti Yoga (devotion), Raja Yoga (meditation) and Jnana Yoga (inner wisdom or enlightenment). These are the classic four yogas within which are several other forms of Yoga. Hatha Yoga (worshipful poses), for example, is part of Raja Yoga training. Some of the other forms of Yoga are Nada Yoga (music), Mantra and Japa Yoga (chanting and on beads) and Kundalini Yoga (study of the psychic centers or chakras).
- Karma-kanda - through selfless activities, and sacred rituals one can enjoy the world to maximum benefit and make material advancement, even reach heavenly planets. This path, however is intrinsically slow.
- Jnana-kanda - through rigorous austerity, asceticism, and study of Vedic texts one learns to detach altogether from the illusory influence of Maya, this path is arduously difficult.
- Bhakti - this is the synthesis of the previous two; in which the individual focuses on love and service to the absolute truth. This way the aspirant remains active in the world without falling prey to the influence of Maya
- Hatha-yoga - Hatha-yoga is an ancient system of techniques used to free the body and mind from tension, stress, illness and disease. The practice combines the use of physical postures (yogasanas), breathing exercises (pranayama) and meditation (dyhana) to develop flexibility, strength and balance. There are many different styles of hatha-yoga, each reflecting the teachings of a particular Master (Guru). Various types of hatha-yoga are Sivananda, Kripalu, Iyengar, Bikram, Kundalini and AtmaVikasa Yoga (to name a few).