In Chinese and other Eastern thought, yin and yang are the two opposing and complementary forces that make up all phenomena of life.
Both proceed from the Supreme Ultimate and together they represent the process of the universe and all that is in it.
The concept of the yin-yang is very ancient, and its precise origins are unknown. In the third century BCE, it formed the basis for an entire school of cosmology, the Yin Yang School.
According to the Encyclopedia Britannica , "The significance of yin-yang through the centuries has permeated every aspect of Chinese thought, influencing astrology, divination, medicine, art, and government."