What are Yin and Yang in Traditional Chinese Medicine?

In the Chinese perspective, given the importance of "taking everything as a whole," all things are relative. A thing can be understood only in relation to something else. This is the essential idea behind the use of the terms yin and yang.

Yin and yang are terms used to describe relative opposite qualities or manifestations of Qi. If yin is form, then yang is function. If yin is material, then yang is immaterial.

• Yin refers to aspects or manifestations of Qi that are relatively material, substantial, condensing, solid, heavy, descending, cold, moist, cooling, dark, passive and quiescent.
  
  
• Yang refers to aspects or manifestations of Qi that are relatively immaterial, amorphous, expanding, hollow, light, ascending, hot, dry, warming, bright, aggressive, and active.