The meridians of the human subtle energy system are pathways through which chi (ki, prana, kundalini, etc.) flows in our body as seen in the illustrations:

The Chinese Did it First

The images above were created by the developers of TCM, Traditional Chinese Medicine. As Dr. Andrew Weil explains, the Chinese developed non-invasive medicine and the West developed invasive medicine. The Chinese discovered how to improve health working with the flow of vital energy without having to cut people open.

In Acupuncture, sterile needles are used to stimulate junction points along the meridians that act as gateways that control the flow of chi, or life force energy. Acupressure (shiatsu) does the same thing without needles using just the pressure of the fingers.

Each pathway outlined and each junction point is associated with a certain organ, emotional state, and beliefs or ways of thinking. It is very similar to the chakra system. By changing the direction of the flow of energy through these points, stimulating energy flow, or slowing energy down, a practitioner can change and heal physical, psychological and emotional states.

Currently acupuncture is used to control pain, heal depression, as anesthesia in surgeries and child birth and much more.

Donna Eden explains how to work with the meridians in maintaining health in her book, "Energy Medicine". It is quite extensive and has amazing tools you can implement on your own without having to see an acupuncturist.

This system is used in EFT

EFT uses the meridian system. During EFT, meridian points are tapped while addressing psycho-emotional issues. By doing this, EFT utilizes the bodies own subtle energy pathways to flush or eliminate negative feelings.