Taiji, the great ridgepole, appears in the Book of Changes as the source of the two modes. Zhou Dunyi and Zhu Xi made it the supreme principle of the cosmos, present whole in each thing. The familiar black-and-white symbol represents it, and the martial art taijiquan is named after it.
Taiji
The supreme ultimate: the source from which yin and yang arise, and in Neo-Confucianism the totality of principle.
Also: Tai chi, Supreme Ultimate