Yin and Yang
Yin and Yang represent the two opposite principles in nature. Yin is the feminine or negative nature of things and yang is the masculine or positive side.
Yin and yang work in pairs, such as hot and cold, female and male, dark and bright. But yin and yang are not static or just two separated things, they interchange and interplay of the two components.
The alternation of hot and cold is such an example - as you add more of one to the other, then a physical change will take place - simple put, adding hot water to a cold water bucket will turn the water warm.
The principles of yinyang are an important part of Huangdi Neijing (Yellow Emperor's Classic of Medicine).
The following ebook will provide a greater knowledge for you of this ancient Yin Dynasty which dates back about 1400 - 1100 BC.