The Meridians are a complex network of channels of energy flow. To put it in another way, they are like the veins and arteries on the energy level. Connecting the chakras, the Tantiens, Aura and its different layers with the rest of the energy system. They also relate to the physical body, because very often the existing blockages in the meridians become physically diseases. Later I will discuss how the disease comes to our body.
Traditional Chinese Medicine is that studies how to unblock meridians through acupuncture and other techniques. Reiki initiations, among other things, clean these channels so that energy can flow freely. However, we must ensure that these channels are clean. To do this, we can assert Reiki energy or to make some kind of Chi Kung exercises. The meridians in India are known by the name of Nadis, and the most important are Ida and Pingala interconnecting the main Chakras.
Here are some pictures with the path that the main meridians follow. If you find interesting this issue, traditional medicine practices such as China or Shiatsu, are dedicated to working with the meridians. Whether putting needles in key energy points of each meridian (acupuncture) or by finger pressure (acupressure). In Reiki is not so important to know the exact layout of each meridian, but it's good that we have any idea about it.