The term refers to the dynamic balance or ordered homeostasis due to the mutual regulation of stable yin and compact yang, which is the basis of normal life activities. According to the theory of yin and yang, man will not be full of vitalities and perform normal life activities unless yin and yang maintain the dynamic balance or ordered homeostasis, i.e., yin essence keeps from consumption and yang qi consolidates. It is because of the integration of yin qi and yang qi within the human body that promotes the mutual conversion between substance and substance, substance and energy, as well as propels and regulates human life processes. At the same time, mutual opposing and constraining, mutual rooting and promoting, waxing and waning, as well as mutual conversion of yin and yang maintain the state of balance so that life activities can be performed orderly, and various physiological functions can be fulfilled stably.