Defining "Qi"

The Chinese word "Qi" is often mistranslated as "energy" in English. "Qi" is not energy.

"Qi" cannotes both substance and function. Substance and function are two different concepts but they are closely related and cannot be entirely separated. This is because each function must be based on a certain substance, while a certain form of substance is bound to demonstrate a corresponding function. -Essentials of Chinese Acupuncture, p. 36

While not easy to translate, a better term than "energy" is "Air" or "Vital Air".