Yin and yang are two powerful opposing but complementary forces and said to be found in all matter and processes, in the universe. As early as the 4th century BC, the Chinese philosophers wrote about yin and yang; Yin being associated with dark, moist, soft, passive, receptive, earthy, and female while yang is associated with everything bright, dry, active, hard, aggressive, heavenly, and male.
The Taijitu, a circle divided into a half white and a half black shape, symbolizes the yin and yang forces. The shapes are not semicircles because, although a constant struggle for balance is ongoing, absolute balance between yin and yang does not exist.
The black dot on the white shape and the white dot on the black shape signify that yin cannot exist without yang nor can yang exist with yin.