Qi, meridians and acupuncture points :

Traditional Chinese medicine distinguishes not only one but several different kinds of qi. In a general sense, qi is something that is defined by five "cardinal functions":

Actuation – of all physical processes in the body, especially the circulation of all body fluids such as blood in their vessels. This includes actuation of the functions of the zang-fu organs and meridians.

Warming – the body, especially the limbs.
Defense – against Exogenous Pathogenic Factors
Containment – of body fluids, i.e. keeping blood, sweat, urine, semen etc. from leakage or excessive emission.
Transformation – of food, drink, and breath into qi, xue (blood), and jinye (“fluids”), and/or transformation of all of the latter into each other.

To fulfill its functions, qi has to steadily flow from the inside of the body (where the zang-fu organs are located) to the "superficial" body tissues of the skin, muscles, tendons, bones, and joints. It is assisted in its flow by "channels" referred to as meridians . TCM identifies 12 "regular" and 8 "extraordinary" meridians; There's also a number of less customary channels branching off from the "regular" meridians. Contemporary research has not supported the existence of qi or meridians.] The meridians are believed to connect to the bodily organs, of which those considered hollow organs (such as the stomach and intestines) were also considered yang while those considered solid (such as the liver and lungs) were considered yin. They were also symbolically linked to the rivers found in ancient China, such as the Yangtze, Wei and Yellow Rivers.

Acupuncture points are mainly (but not always) found at specified locations along the meridians. There also is a number of acupuncture points with specified locations outside of the meridians; these are called "extraordinary" points and often credited with special therapeutic properties. A third category of acupuncture points called "A-shi" points have no fixed location but represent tender or reflexive points appearing in the course of pain syndromes. The actual number of points have varied considerably over time, initially they were considered to number 365, symbolically aligning with the number of days in the year (and in Han times, the number of bones thought to be in the body). The Huangdi Neijing mentioned only 160 and a further 135 could be deduced giving a total of 295. The modern total was once considered 670 but subsequently expanded due to more recent interest in auricular (ear) acupuncture and the treatment of further conditions. In addition, it is considered likely that some points used historically have since ceased being used.

The acupuncturist decides which points to treat by observing and questioning the patient in order to make a diagnosis according to the tradition which he or she utilizes. In TCM, there are four diagnostic methods: inspection, auscultation and olfaction, inquiring, and palpation.