What is the meaning of Yin and Yang?

Yin and Yang  are the two polarities of the Chi. Pairs of opposites are often used to illustrate like "active and passive", "light and dark" or even "male and female".

The genesis of Yin and Yang

In the beginning there was nothingness, the great undivided emptiness, the mother of all beings and things, Wuji.

From the Wuji emerged the five phases of transformation, better known as Five-Elements-Cycle in the transformation of yin and yang. Taiji is the birth of duality, the division of the whole.

The duality manifests itself in space = matter and time = energy

Yang, the active pole is equivalent to time and energy. Energy can also be translated with spirit or intention. Yin, the passive pole is equivalent to space and matter. By the way, Einstein's formula e = mc²  proves exactly that matter and energy are equivalent.

When you encounter Feng Shui books, consultants, and websites that deal exclusively with matter and decoration, you now know that this is not authentic Feng Shui, but the superficial New Age Commerce that we describe in our Sheng Yuck category. 

The representation of yin and yang with barcodes was already used in I-Ching, one of the world's oldest wisdom books and the basis of the Imperial Feng Shui we work with. 

Yin and Yang are complementary and not counterparties

The two complementary forces Yin and Yang are interdependent and complement each other. They exchange their energy permanently whereby new Chi arises. Balance of Yin and Yang in Feng Shui does not mean that the ratios are 50:50, that would be deadlock. Balance means that a yang phase is followed by a yin phase, just like the night follows the day.

The unity of polarity is a central tenet of Daoism, the Chinese philosophy from which Feng Shui emerged. It means that the whole is always more than the sum of its parts.