What is Qi?

The vital life force in the body, supposedly able to be regulated by acupuncture. It corresponds roughly to the Greek pneuma, the Latin spiritus, and the ancient Indian prana. The concept of life-breath or vital energy was formulated as an indication of the awareness of man, originally directed externally toward nature or society but later turned inward to the self or life within. (From Comparison between Concepts of Life-Breath in East and West, 15th International Symposium on the Comparative History of Medicine - East and West, August 26-September 3, 1990, Shizuoka, Japan, pp. ix-x)