This term refers to sounds produced by all things in nature between heaven and earth. Zhuangzi (369?-286 BC) divided sounds into three categories: “human sounds,” “terrestrial sounds,” and “celestial sounds.” According to him, “human sounds” refer to sounds made by a vertical bamboo flute when a person blows air into its top end. “Terrestrial sounds” refer to sounds produced by the earth’s apertures when wind blows through them. “Celestial sounds” are not totally different from the above two. They refer to multifarious sounds made naturally by all things in the universe, which are not sounds created by external factors. By defining the “sounds of nature” this way, Zhuangzi meant to minimize the influence of the subjective mind so as to discover and respect the natural state of all things. People of later generations generally use this term to describe a literary work such as a poem or an essay that is written in a smooth way and has the appeal of natural charm. They also use the term “music of Nature” to refer to naturally produced sounds that are pleasant to the ear.

Ziyou said: “‘Terrestrial sounds’ are those produced by the earth’s apertures; while ‘human sounds’ are those that come from a vertical bamboo flute. What then are ‘celestial sounds’?” Ziqi answered: “When the wind blows across the land, it makes a myriad of different apertures produce varied sounds. Such sounds are made naturally by those apertures. What else could rouse them to create such sounds?” （Zhuangzi）