What is yin and what is yang? In a word, yin is just like the water. So if one thing is agglomerate, wet and restraining as water is called yin, such as the moon, the earth, night, cold,and all materiality. These are dark, quiet, heavy, inside and low. Yang is just like the fire. So if one thing is hot, dry, ascensive can be called yang. For example, the sun, the sky, day, warm and all immateriality. These are bright, move, light, outside and up.
So in human body, back, energy, body surface, up of the body, outside of the body, governor meridian, function, active is yang, abdomen, blood, inner, low of the body, inside of the body, concepion meridian material, inactive is yin.