The concept of Meridian in TCM

Meridians or "经络 Jing Luo" in Chinese is a general term for meridians and collateral. They are types of pathways where the circulation of human qi (life force/energy) and blood occurs. These pathways make up a comprehensive yet complex body map that supplies vital energy to every part of the body. TCM primarily works with 12 basic meridians plus two special ones. There are more than 14 meridians, but the other meridians rarely are used by most TCM healers.
If you see the human body as a tree, then visualize the meridians as the main trunks, which run longitudinally. Collateral are the branches of meridians running reticular over the body. Meridians run through our physical bodies but they cannot be dissected or found surgically. They are part of the body’s subtle energy anatomy and have no concrete form. The entire system of meridians and collateral connect internally to the organs and externally to the skin and muscles. Through this system the body's tissues are linked together as an organic whole.
Therefore the concept of the meridian system is a network of life force channels, where blood is circulated and subtle energetic events occur. In Traditional Chinese Medicine, acupuncture is applied to points on the meridians to release blockages and bring about healing of all kinds, while key points are used by traditional doctors to diagnose health and balance in the body’s systems.