"Nadi" means “channel”. Nadis are the subtle (spiritual) nerves corresponding with the physical nerves, through which, in traditional Indian medicine and spiritual science, the energies of the subtle body are said to flow. They connect at special points of intensity called chakras. Nadis correspond to the meridians of traditional Chinese medicine. There are thousands of nadis in the body, but only a few are deliberately purified and opened to achieve the broad effects of yoga throughout the entire nervous system. They all start from the central channel of the chakras to the periphery where they gradually become thinner.
Nadis are thought to carry a life force energy known as prana in Sanskrit, or Qi in Chinese-based systems. They are also said to have an extrasensory function, playing a part in empathic and instinctive responses.
Nadis are sometimes viewed as extending only to the skin of the body, but are often thought to extend to the boundary of the aura.
Click on "Main Lessons" above to learn purification of the main nadis or read more here: Lesson 125 - Kundalini heat