(Tai Yi)
The Great Duality

The Chinese word "Tai" means great, and "Yi" means second (two). The state of the "Great Duality" is described in the Taoist classic "Direct Instruction to the Great Elixir" or "Dadan Zhizhi"  by Qiu Chuji , the third patriarch of the  Quanzhen School  and the founder of the Longmen School  (which is the prevailing Taoist school in the world nowadays), as the state where:

"... inside no body is awared, outside no cosmos is awared, being one with Tao ... can not get its name, forced to name and say it as the Great Duality ... is the mother of the golden elixir."