The yin-yang diagram represents the ceaseless flow, or interplay, of the two fundamental and complementary aspects underlying all phenomena. Yin is the potential, yang the expression.
The Ba gua, or Eight Trigrams, are composed of a combination of broken and unbroken lines. The broken lines represent yin and the unbroken yang. The eight trigrams represent every permutation, or possible combination, of yin and yang that can occur in a pair of three. As yin and yang are representative of the fundamental complementary aspects underlying all phenomena, the eight trigrams are a way of representing all possible phenomena in existence.
Yin-yang and the ba gua combined create a simple, concise symbol that represents the basic nature and manifestation of nature and existence, and is used extensively through out the traditional Chinese arts.