Prana Energy

If you allow yourself to be guided by the invisible energies within yourself, before you know it, you will feel the flow of Chi, Prana or Life Energy within you and understand what is good for you and what you need to heal and grow and achieve happiness and inner peace.

Scroll down the page of this Encyclopedic Theosophical Glossary and you'll find a splendid definition of prana. It leans toward the esoteric.

Robert Todd Carroll has little to say about prana in the Skeptic's Dictionary. He mentions that it's like chi, which he does speak on at length.