Yin and Yang
Yin and Yang are universal principles of order. The One is not without the other. Everything that exists and changes, arises in the interplay of yin and yang. In the Chinese character Yin represents a hill with shadow side, the Yang a hill with sunny side. Although yin and yang opposites characterize (shadow - light, cold - heat, water - fire), they are not mutually exclusive; they rather complement each other. Although, for example, day and night opposites, but flow together seamlessly: The day is only through the night a day.
Yin and Yang as part of the TCM
The idea of yin and yang found its way into the Chinese medicine. Disturbances in the balance of yin and yang are the foundation of TCM. If the Yang is rising in the body for example, it is called an excessive-heat syndrome. Is the Yang decreasing, the person suffers from a deficiency-cold syndrome. Goal of the TCM is to bring yin and yang in a balance.