हथ - haṭha (pronounced 'ha-tah') ~ force
'Haṭha' is a sanskrit word meaning ‘force', and was traditionally used to indicate an energetic quality of the effects of its many practices. Within popular yoga folklore, the term Haṭha is often associated with the reconciliation of solar and lunar energies within the subtle body, which is a central theme of the practice. 'Ha' is believed to indicate the Sun and 'Ṭha' the moon.
Haṭha yoga is a path of physical transformation & spiritual emancipation in which the body is utilised as a tool towards the goal of 'mokśa' - liberation. Haṭha yoga originally developed in the 9th -10th century and was a synthesis of Tantra and Asceticism, that consolidated a vast spectrum of techniques broadly focused upon: containment of subtle energy and the awakening of potent spiritual energy - ‘kuṇḍalinī śakti.’ The pioneers of haṭha yoga were ascetics living on the fringes of Indian society. Initially, their teachings were transmitted orally, and then from the eleventh century were recorded in sanskrit texts.
Although interest in haṭha yoga declined in the eighteenth and nineteenth centuries, the twentieth century heralded a new renaissance in which innovative teachers such as T. Krishnamarcharya, Swami Kuvalayananda and Swami Sivananda combined haṭha with Pātañjala yoga, Neo-Vedānta and Tantra.
Today haṭha yoga enjoys widespread popularity accross the globe. A variety of styles and interpretations have emerged and many of the the earlier, more esoteric elements of the the practice have been discarded in favour of an approach based upon wholeness, health and well being. The 'āsana' - postures from the haṭha tradition have today become a iconic symbol of yoga.
The signs of success in Haṭha Yoga are slenderness of the body, a cheerful face, hearing of the mystical sound, bright eyes, freedom from dis-ease and a sense of well-being.
Svātmārāma ~ Haṭha Pradīpikā 2.78