Yin and Yang 

Eastern thought, the two complementary forces that make up all aspects and phenomena of life. Yin is a symbol of earth, femaleness, darkness, passivity, and absorption. It is present in even numbers, in valleys and streams, and is represented by the tiger, the colour orange, and a broken line. Yang is conceived of as heaven, maleness, light, activity, and penetration. It is present in odd numbers, in mountains, and is represented by the dragon, the colour azure, and an unbroken line. The two are both said to proceed from the Great Ultimate (taiji), their interplay on one another (as one increases the other decreases) being a description of the actual process of the universe and all that is in it. In harmony, the two are depicted as the light and dark halves of a circle.