Depending on perspective and location, yoga can be a spiritual discipline and form or religious meditation, an exercise practice, or a bit of both. It is usually recognized as a set of incrementally difficult stretches that blend muscular flexibility with deep breathing, and there are several different variations each with different goals. In much of the West, it's thought of as a form of exercise; classes are frequently offered by gyms and fitness centers, and most attendees participate as a way to improve their strength and cardiovascular health. Some also like the peacefulness and the focus on deep breaths and calming the body. The practice originated in India as a means of religious meditation, and that dynamic of the practice can be equally if not more important for many of the most serious devotees. A lot depends on perspective and approach.
Origins
No one is entirely sure when or where the practice began, although it's widely believed to have originated in India. The Yoga Sutra by Patanjali, a 2,000 year old work, is the first written mention of the practice. Previous to this, it was an oral tradition passed from person to person. The practice continues to be most popular in India. The religious elite may have made the discipline famous, but as a form of meditation it is available to all. It is most commonly associated with Hinduism and is often used as a tool or essential element in clearing the mind to communicate with and be receptive to the spiritual realms embraced by that faith tradition.
Philosophy and Religious Aspect
The practice is an important part of the Hindu faith. Hinduism is based primarily on a set of sacred texts known as the Vedas, but also includes six distinct schools of thought — one of which is yoga. In a very general sense, practitioners of this variety of stretching and meditation are attempting to control their senses, their minds, and their bodies in order to being them in line with the purity needed for moksha, which is usually thought of as a oneness with the Divine or the Supreme Being embraced by the faithful.
As an Exercise Discipline
Particularly in the West, many of the people who participate in yoga or who attend classes don’t do so as a means of religious practice. Many appreciate the spiritual aspects and find some benefit in the meditative nature of the exercises, but those who aren’t Hindus aren’t usually trying to use the stretches and poses for the same end goals, which necessarily alters the core definition of what the practice is.
Primary Variations
There are many different schools of traditional practice, all of which have their own unique poses and philosophies. Below are five of the most common, although schools and paths have been established with many different variations that aren't listed here. Some are even based on a particular instructor's habits and teachings. All can be used either as sacred practice or as exercise, and are often available as classes or in group settings. People who are familiar with the core teachings can of course also practice independently. Those who are looking for more formal classes are usually wise to familiarize themselves with some of the core variations in order to find a course that meets their needs.
Hatha is a very popular variety, and one that has been commonly taught for years. The main focus is usually on perfecting the mind by way of perfecting the body. Many asanas, or moments of sitting still, are used; breathing techniques and meditations are also central.
Ashtanga is a type of hatha yoga. Meaning "eight limbed yoga," it consists of postures using the different limbs. Like all yoga, ashtanga is based on principles and is a mental and spiritual exercise as much as it is a physical one.
Kundalini is centered on awakening and focusing what is known as kundalini energy. In most of the literature, kundalini energy is most easily compared to life energy that lies dormant in the body. It is commonly represented by a coiled snake.
Mantra practitioners primarily devote themselves to calming the mind and body through the use of words and sounds. The well-known "om" chant is commonly heard in this school.
Tantra is known by way of its focus on sexual spirituality. Practitioners also focus on kundalini energy, although their intent for awakening it is usually much different from the Kundalini practice.