Chi is the concept of "Universal Energy" which is predominate in Chinese philosophy. It's a metaphysical concept dealing with life energy, the idea being all living things have chi.
Many believe that this energy can be manipulated and even harnessed. For many Chinese Martial Arts, the idea is to learn to channel your chi to be stronger, quicker, harder through meditation, concentrations, etc..
My experience has been that a good armlock seems to work regardless of how strong a person's chi supposedly is!
