Yin and Yang is a pair of categories belonging to ancient Chinese philosophy, which is a generalization of the attributes of the two opposing sides of some interrelated things and phenomena in the natural world. Yin and yang can denote both opposing things and phenomena, as well as two opposing aspects within the same thing or phenomenon. Generally speaking, what is bright, moving, outward, rising, diffuse, warm and exciting is Yang, and what is relatively still, cold, obscure, inwardly guarded, descending, cohesive and inhibiting is Yin. There is a certain relationship between yin and yang. Yin and yang are opposites and constraints, yin and yang are mutually rooted and utilized, yin and yang are sympathetic and mutually hidden, yin and yang can be eliminated and balanced, and yin and yang can be transformed into each other.