Yin Yang is perhaps the most known and documented concept used within Taoism.
A starting definition: Yin / Yang : Two halves that together complete wholeness. Yin and yang are also the starting point for change. When something is whole, by definition it is unchanging and complete. So when you split something into two halves – yin / yang, it upsets the equilibrium of wholeness. This starts both halves chasing after each other as they seek a new balance with each other.
The word Yin comes out to mean “shady side” and Yang “sunny side”.
Yin Yang is the concept of duality forming a whole. We encounter examples of Yin and Yang every day. As examples: night (Yin) and day (Yang), female (Yin) and male (Yang). Over thousands of years quite a bit has been sorted and grouped under various Yin Yang classification systems.
The symbol for Yin Yang is called the Taijitu. Most people just call it the yin yang symbol in the west. The taijitu symbol has been found in more than one culture and over the years has come to represent Taoism.