The original meaning of Yin-Yang was the bright side- dark side. Yang is the bright side and Yin is the dark side. Everything in the world can be described, explained and further divided into the Yin-Yang phenomena.
The basic properties of heat, brightness, activeness, outwardness, upwardness, hyper function belong to Yang. The basic properties of coldness, darkness, stillness, inwardness, downwardness, hypo function belong to Yin.
Yin and yang oppose each other and at the same time have an interdependent relationship. Without Yang there is no Yin, without Yin there is no Yang.