The word yoga means "union" in Sanskrit, the language of ancient India where yoga originated. We can think of the union occurring between the mind, body and spirit. What is commonly referred to as "yoga" can be more accurately described by the Sanskrit word asana, which refers to the practice of physical postures or poses. Asana is only one of the eight "limbs" of yoga, the majority of which are more concerned with mental and spiritual well being than physical activity. In the West, however, the words asana and yoga are often used interchangeably.

Yoga Poses
Many people think that yoga is just stretching. But while stretching is certainly involved, yoga is really about creating balance in the body through developing both strength and flexibility. This is done through the performance of poses or postures, each of which has specific physical benefits. The poses can be done quickly in succession, creating heat in the body through movement (vinyasa-style yoga) or more slowly to increase stamina and perfect the alignment of the pose. The poses are a constant, but the approach to them varies depending on the tradition in which the teacher has trained.

Hatha Yoga is a particular system of Yoga described by Yogi Swatmarama, compiler of the Hatha Yoga Pradipika in 15th century India. Hatha Yoga differs substantially from the Raja Yoga of Patanjali in that it focuses on shatkarma, the purification of the physical body as leading to the purification of the mind (ha), and prana, or vital energy (tha). Compared to the seated asana, or sitting meditation posture, of Patanjali's Raja yoga,it marks the development of asanas (plural) as full body 'postures' now in popular usage.
Hatha Yoga in its many modern variations is the style that many people associate with the word "Yoga" today.Because its emphasis is on the body through asana and pranayama practice, many western students are satisfied with the physical health and vitality it develops and are not interested in the other seven limbs of the Raja Yoga tradition.

Yoga practices in other traditions
Although Yoga has basically been a Hindu practice, its elements have crept throughout the world and major religions like Buddhism, Jainism, Sufism, all being mystic religions, have embraced the practice as being a holy one.

Yoga and Sufism
The development of Sufism was considerably influenced by Indian yogic practises, where they adapted both physical postures (asanas) and breath control (pranayama). The ancient Indian yogic text, Amritakunda, ("Pool of Nectar)" was translated into Arabic and Persian as early as the 11th century.

Yoga and Buddhism
Yoga is intimately connected to the religious beliefs and practices of the Indian religions.The influence of Yoga is also visible in Buddhism, a descendant of Hinduism, which is distinguished by its austerities, spiritual exercises, and trance states.

Yogacara Buddhism
Yogacara (Sanskrit: "Practice of Yoga [Union]"), also spelled yogāchāra, is a school of philosophy and psychology that developed in India during the 4th to 5th centuries.
Yogacara received the name as it provided a yoga, a framework for engaging in the practices that lead to the path of the bodhisattva. The Yogacara sect teaches yoga in order to reach enlightenment.

Ch'an (Seon/Zen) Buddhism
Zen (the name of which derives from the Sanskrit "dhyana" via the Chinese "ch'an") is a form of Mahayana Buddhism. The Mahayana school of Buddhism is noted for its proximity with Yoga. In the west, Zen is often set alongside Yoga; the two schools of meditation display obvious family resemblances. This phenomenon merits special attention since the Zen Buddhist school of meditation has some of its roots in yogic practices. Certain essential elements of Yoga are important both for Buddhism in general and for Zen in particular.

Tibetan Buddhism
Yoga is central to Tibetan Buddhism. In the Nyingma tradition, practitioners progress to increasingly profound levels of yoga, starting with Mahā yoga, continuing to Anu yoga and ultimately undertaking the highest practice, Ati yoga. In the Sarma traditions, the Anuttara yoga class is equivalent. Other tantra yoga practices include a system of 108 bodily postures practiced with breath and heart rhythm. Timing in movement exercises is known as Trul khor or union of moon and sun (channel) prajna energies. The body postures of Tibetan ancient yogis are depicted on the walls of the Dalai Lama's summer temple of Lukhang. A semi-popular account of Tibetan Yoga by Chang (1993) refers to Dumo, the generation of heat in one's own body, as being "the very foundation of the whole of Tibetan Yoga" (Chang, 1993, p7). Chang also claims that Tibetan Yoga involves reconciliation of apparent polarities, such as prana and mind, relating this to theoretical implications of tantrism.

Goal of yoga
The goal of yoga may range from anywhere between improved health and reaching Moksha. Within the monist schools of Advaita Vedanta and Shaivism the goal of yoga takes the form of Moksha, which is liberation from all worldly suffering and the cycle of birth and death (Samsara), at which point there is a realisation of identity with the Supreme Brahman. In the Mahabharata, the goal of yoga is variously described as entering the world of Brahma, as Brahman, or as perceiving the Brahman or Atman that pervades all things. For the bhakti schools of Vaishnavism, bhakti or service to Svayam bhagavan itself is the ultimate goal of the yoga process, wherein perfection culminates in an eternal relationship with Vishnu, Rama or Krsna.