The term refers to a state of mind totally free from all constraints. It was first proposed by Zhuangzi (369?-286 BC) in one of his most well-known essays. According to him, people’s minds can go beyond predicament in a way that their bodies cannot, so mentally they can be independent of material concerns and free of all worries. Guo Xiang (?-312) of the Western Jin Dynasty had a new definition of the term: By acting in accordance with its own nature, everything can be free of troubles and worries.

People should seek carefree enjoyment beyond the constraints of the human world. (Zhuangzi)

Things, big and small, are different from each other. But when they are placed where they should be, each of them will develop as its nature dictates, shoulder their proper responsibilities, and ultimately achieve the same degree of freedom. (Guo Xiang: Annotations on Zhuangzi)