It is understood in TCM that the meridians (jing) and collaterals (luo) are pathways in which the qi and blood of the human body are circulated. They form a specific network which communicate with the internal organs and limbs and connects the upper to the lower and the exterior to the interior portions of the body. The meridians are the major changes of the system and they run lengthwise within the interior of the body. The collaterals are the branches of the meridians and they run crosswise from the meridians either on or just below the body's surface. Since they are distributed over the entire body, the meridians and collaterals link together the zang-fu(internal organs of human body) and other organs, the orifices of the body, then the skin, muscles and bones. They bring the body into an organic whole to carry on systematic activities.

The theory of the meridians and collaterals studies the physiological functions and pathological changes of the meridian system, as well as the relationship between the system and the zang-fu organs(internal organs) . It is an important component of the theoretical system of traditional Chinese medicine (TCM). The theory of meridians is closely related to acupuncture therapy. It provides not only the theoretical foundation for acupuncture, moxibustion, massage and qigong, but also guides the clinical practice of other related fields of TCM.