The term “qi” is a concept, it is an approximation, just as all of our scientific models are, and its utility in the context of traditional Chinese medicine (TCM) is indisputable. The mystery of the qi concept has been a stumbling block for the acceptance of TCM and acupuncture into the modern sciences for decades. This lecture presents a rational approach to understanding the qi concept, and explores its usefulness as a qualitative term for describing the functional quality of living tissue. By examining the traditional  application of specific botanical medicines that are defined as affecting the qi of the body directly, we can gain further insight into what “qi” is, and how to work with it to help the body maintain homeostasis. 

If you would like to read a bit more, here is an introductory paper with more info.