With ha meaning "Sun" and tha meaning "Moon", hatha yoga is commonly translated as the yoga that brings "Union of the pairs of opposites". Sometimes Hatha Yoga is also translated as the "forcefull yoga", because it seems to require the most physical excercises of all yoga types. Hatha Yoga is certainly the yoga that is the best known in the West, which is probably why so many definitions of Hatha Yoga exist.

In the indian tradition, hatha yoga is one of the four main traditions of Tantra Yoga. Hatha Yoga is first of all concentrating on the practice of postures (asanas) and breath control (pranayama) to energize the subtle channels (nadis). Thus Hatha Yoga concentrates on the third and fourth steps of the eight-fold path of Ashtanga Yoga. The objective of Hatha Yoga is obviously to remove the obstacles to address the further steps of Pratyahara (sense-withdrawal), Dharana (Concentration), Dhyana (Meditation) and Samadhi (Balance). In many hatha yoga schools, these further steps are seen as part of Hatha Yoga. What's in a name ?
Excercising postures or Asanas in Hatha Yoga has two essential objectives. The first is that to practice any real meditation, one needs at the least one posture in which one can be perfectly comfortable for a longer period of time. The more such postures one can master, the better the basis for developing the inner meditation techniques. The second objective of excercising asanas in Hatha Yoga is to bring health and energy to body and mind by opening the nadis. When such excercises are regularly perfomed, the path of hatha yoga is opened automatically, though one still has to follow it further. The mere mastering of postures is no objective in itself, though mastering various postures certainly strengthens the power of will and concentration and the habit of not paying too much attention to the information input by the senses. Thus practicing asanas in Hatha Yoga directly opens the path to Prathyahara and Dharana.