Chi or Ki energy refers to the "life force energy of the body.
Chi is an electrical current that runs on the outside of the nerves because of an electric principle called induction. Very similar to a transformer.
Proper Chi flow in the body is a result of good health and proper functioning of the body systems. And Vice-Versa. This is the basis of Chinese medicine and acupuncture. Acupuncture corrects body health by reestablishing proper chi flow. Each systems affects the other systems. The explanation is over simplified, but I know you get the idea!