Hatha yoga

Hatha Yoga Pradipika emphesis that the science of Hatha yoga is only for sake of Raja yoga. Grossest meaning of Hatha is force, or forcing,  because initially in hatha we force ourselves to break old body habits. Later when we deepen our practice and start understading the subtle force of our body meaning  of Hatha got changed into Ha and Tha. Ha is solar `energy within body and Tha is lunar energy of the body. When these two opposite energies got balaned and inter into thirt energy channel called Susumna.