It refers to the constant nature or regular pattern of natural laws. The ancient Chinese believed that phenomena in the universe and life in human society are governed by constant laws in their movement. People characterize these laws as being "constant" and sometimes call them "constant ways" or "constant principles." "Constant" is in contrast to "change," but it is also closely connected with "change." Given that these are the natural laws or patterns that phenomena follow, they are stable and unchangeable. But these constant natural laws are manifested through myriad changing things. It is by learning about continuous changes that people seek to identify and comprehend underlying constant laws or principles.

Nature's ways are constant. They did not exist because Yao was on the throne or disappear because Jie was the ruler. (Xunzi)

Things in nature are numerous and diverse and will eventually return to their roots. Returning to one's root is reaching tranquility. To reach tranquility is to go back to the original state of life. Going back to the original state of life is returning to the constant. Knowing what is constant is called wisdom. (Laozi)