Vital energy refers to the finest and most subtle energy. The earliest detailed explanation of vital energy is found in Guanzi. According to the book, the finest and most subtle energy is a concrete manifestation of dao. All things with shapes and all human beings are made up of vital energy; one’s life, sense, and intelligence are also believed to derive from vital energy.

Everything is generated by its vital energy. Vital energy produces crops on the earth and forms stars in the sky. When vital energy comes between heaven and earth, it creates ghosts and spirits; when it goes into the heart of a human being, a sage is created. (Guanzi)

People depend on vital energy for survival. When they die, their vital energy vanishes. (Wang Chong: A Comparative Study of Different Schools of Learning)