The word hatha is a compound of the words ha and tha meaning sun and moon, referring to prana and apana, and also to the principal nadis (energy channels) of the subtle body that must be fully operational to attain a state of dhyana or samādhi. Hatha yoga also called hatha vidya is a system of yoga introduced by Yogi Swatmarama, a sage of 15th century India, and compiler of the Hatha Yoga Pradipika.
Hatha yoga is one of the two branches of yoga that focuses on the physical culture, the other one being raja yoga. Both of these are commonly referred to as sadanga yoga, i.e., yoga of six parts ('sad' meaning six and 'anga' meaning limbs).
The Six Limbs of Yoga are:
Asana (bodily postures) strengthen the body by muscular build up, activate the glands and organs, create strength and endurance. The body is made flexible and smooth by stretching of the tendons and ligaments. The joints are strengthened, the metabolism is activated and the body detoxified.
Pranayama (breath control) quietens the mind, and leads to inner balance. By breathing the body is supplied with life force and therefore breath control influences the body's overall energy system. The coordinated interaction of breathing and body postures deepens the practice of Asana, leading to relaxation and de-stressing. The inner peace derived through this method prepares the foundation of the practice of the third limb of Shadanga yoga.
Pratyahara (composure) the third limb, allows Self reflection. By the practice of Asana and Pranayama the mind is quietened and awareness is liberated from distracting external influences, the mind is at rest and concentration is trained. The ability to resolve conflicts is heightened and aggression is reduced. Pratyahara is the foundation of the other stages of the mental training of Yoga.
The next two stages are Dharana (concentration) and Dhyana (immersion). They are taught when the student is prepared by prolonged practice of the prior three limbs. These meditative absorptions liberate the mind from traumatic burdens (Samskara) and impurities (klesha), and are enabling the attainment of inner peace. The highest stage, Samadhi (union) fully liberates the mind from its individual limitations.