"The three pure ones". The name of the three Taoist heavens and the three deities inhabiting them. The first of these heavens is Yu-qing, the Heaven of Jade Purity, and is inhabited by Yuan-shi tian-zong. According to some sources, this first and highest heaven is also ruled by Yu-huang. The second heaven is called Shang-qing, the Heaven of Great Purity, and is reserved for Ling-bao tian-zong. The third heaven is Tai-qing, the Heaven of the Highest Purity. It is ruled by Tao-de tian-zong.