Yin 
Yin is one half of the Tai Chi. The feminine and negative principle (as in rest, darkness and cold) in nature that according to traditional Chinese cosmology interacts with its opposite, Yang, to produce everything that comes into existence.
The phases of interaction are:
- Opposition.
- Interdependence.
- Mutual consumption.
- Inter-transformation.
In the context of Chinese medicine it corresponds to:
- Front.
- Inferior (area below the waist).
- Interior (organ structure and bones).
- Blood and body fluids.
- The Five Zang Organs – Heart (+ Pericardium); Lung; Liver; Spleen; Kidney
- (Nutritive Qi).
- Structure.
- Cold and dampness.
In nature it corresponds to:
- Material.
- Matter.
- Contraction.
- Descending.
- Darkness, moon and shade.
- Earth.
- Space.
- Conservation, storage and sustainment.