This term means six different forms of qi (vital force). Their earliest mention is found in Zuo’s Commentary on the Spring and Autumn Annals. Qi is the basic element of all things corporeal, and flows between heaven and earth. It manifests itself in six different forms: yin, yang, wind, rain, darkness (night), and light (day). They appear in pairs of opposites: yin versus yang, wind versus rain, and darkness versus light. Their interaction produces complicated and varied forms of human and other natural phenomena.

There are six forms of qi, which produce five kinds of smells, manifest in five colors, give rise to five sounds, and if used to excess cause six kinds of illnesses. The six forms of qi are yin, yang, wind, rain, darkness, and light, which spread out into four seasons, and they are aligned to produce the rhythms of the five elements. (Zuo’s Commentary on the Spring and Autumn Annals)

The general population experiences emotions of love, hate, delight, anger, sadness and joy, These six emotions originate from the influences of six types of qi, namely yin, yang, wind, rain, darkness, and brightness. (Zuo’s Commentary on the Spring and Autumn Annals)