In Chinese culture, Yin and Yang represent the two opposite principles in nature. Yin characterizes the feminine or negative nature of things and yang stands for the masculine or positive side. Yin and yang are in pairs, such as the moon and the sun, female and male, dark and bright, cold and hot, passive and active, etc. But yin and yang are not static or just two separated things. The nature of yinyang lies in interchange and interplay of the two components. The alternation of day and night is such an example.

The principles of yinyang are an important part of Huangdi Neijing (Yellow Emperor's Classic of Medicine), the earliest Chinese medical book, written about 2,000 years ago. They are still important in traditional Chinese medicine and fengshui today.

Here is a summary of the characteristics of yinyang. Yin and yang are opposite in nature, but they are part of nature, they rely on each other, and they can't exist without each other. The balance of yin and yang is important. If yin is stronger, yang will be weaker, and vice versa. Yin and yang can interchange under certain conditions so they are usually not yin and yang alone. In other words, yin can contain certain part of yang and yang can have some component of yin. It is believed that yinyang exists in everything.