”Qi” is one of the most important concepts in Traditional Chinese Medicine. Because of this, it has recently become a popular subject of study among scientists and is being researched using modern scientific methods in order to determine its true nature.However, very few people have examined the original literatures of Chinese medicine such as the Nei-Jing, hence it has not yet been possible to properly define ”Qi”.The first reference to internal and external ”Qo” can be found in the Nei-Jing (Yellow Emperor's Classic of Internal Medicine). We have studied the information provided in the Nei-Jing and made a comparative study with contemporary Western concepts of medicine. After analysing the two, the following conclusions can be drawn: 1. Every living organism has ”Qi”. There are 441 different forms of ”Qi”, existing as internal or external manifestations of ”Qi”. 2. The external ”Qi” is divided into Heavenly ”Qi” and Earthly ”Qi”. The Qi that exists inside the organism is known as Life-Qi. 3. From Nei-Jing Lingshu chapter 30, the meanings of Life-Qi are divided into narrow and wide senses, i.e., (1) The narrow sense of Life-Qi is Wei-Qi (lymphatic fluid). (2) The wide sense of Life-Qi includes Wei-Qi, blood, Jing (semen), Jin (sweat), Ye (cerebrospinal fluid, synovial fluid, ……), etc.. We have mentioned Jing, un, Ye, blood, Wei Qi etc.. These concepts are all described in the Nei-Jing Lingshu chapter 30(決氣篇). This chapter leads us to conclude that the Qi concept represents the various body fluids.