The term refers to a state of existence which is hard to see and ascertain. It is used in Laozi to describe the existential characteristics of Dao. According to Laozi, Dao is shapeless, nebulous, and beyond characterization by anything physical or material. At the same time, it is not completely void, but influences everything in the universe. This intangible nature is typical of Dao.
Great Virtue is derived from Dao, which is intangible. Dao embodies physical objects and beings in its intangible existence and captures their essence truthfully in an insightful, meaningful, and credible way. Dao has been in existence since ancient times. It sheds light on the origin of things. How do I come to know the original state of everything? By studying Dao. (Laozi)