Hatha Yoga

Ha = Sun, Tha = Moon

Hatha is what the Western Culture conceptualizes as Yoga, which is erroneous. Hatha is a physical practice that involves special poses or Asanas. These Asanas are very ancient and stem from ancient vedic scriptures. The Hatha Yoga Pradipika is a refference for yoga asanas (fix this up a bit).

There are many forms of physical yoga practiced these days, due to different teachers teaching students who go on to put their own little twist on it. List of some known ones:
 * Ashtanga
 * Anusara
 * Kripalu
 * Bikram
 * Hatha-Raja
 * Jiva Mukti
 * Kundalini
 * Power Yoga

Hatha yoga is just one form of many practices in the Yogic Science.