HA is the masculine or Sun energy and THA is the feminine or Moon energy, a combination of two Sanskrit words. Ida Nadi and Pingala Nadi, are the two main energy channels in the body. Ida is the the moon energy channel and Pingala in the sun channel. When these are balance, an inner peace and contentment is experienced. All yoga, when taught and practiced with awareness, will help create this balance in our energetic system, and so all yoga is Hatha Yoga.
Hatha Yoga is the practice of bringing balance to these two opposing forces. Hatha Yoga is also widely referred to as certain body postures as outlined in classical yogic texts – The Hatha Yoga Pradipika, Gheranda Samhita and The Siva Samhita. These yogic practices are all for the purpose of reaching a deep meditative absorption known as Samadhi. So when we practice Yoga, we strengthen the body so one is able to hold a comfortable and stable position to allow for this absorption – Samadhi.