Hath yoga is a particular system of Yog described by Yogi Swatmarama, a yogic sage of 15th century in India, and compiler of Hath Yog Pridipika. Hath Yog is development –but also substantially from—the Raja Yog of Patanjali, in that it focus on sahtkarma, the purification of physical as leading the purification of the mind( ha), and prana, or vital energy (tha). The meaning of Hath Yoga is usually translated as the Yoga that bringing harmony main energy in human body as “Ha” means sun(pingla nadi) and “tha” means moom(ida nadi). The purpose of Hath Yoga is to locate and activate the chakras(channels if energy in body), thereby raising the kundalini: dominant spiritual power. In contrast, Raja Yog of Patanjali begins with purification of the mind (yamas) and spirit(niyamas), then comes to body via asna (body posture) and Pranayama(breathing). Hath yog contains substantial tantric influence, and mark the first point at which chakras and kundlini were introduced into the yogic canon. Compared to the seated asna of Patanjali’s Raja yog which seen largely as a means of asanas as fully body postures in the modern sence.
Hath yog in its many modern variations is the style that most people actually associate with the word “Yog” today. Because emphasis on the body through asana and Pranayma practice, many western students are satisfied with the physical health and vitality it develops and are not interested in the other six limbs of complete Hath Yog teaching, or with the even older Raja Yog tradition it is based on.