Chi is the Taoist word for the primal energy of Nature which permeates all of creation. It is the vital life force within each of us. Long ago the great sages of China sought to cultivate chi in all of its manifestations. Kung means "training". Hence, chi kung is a generic term roughly translated as "energy training".
Chi kung is also referred to as qigong, but don’t be confused. Both terms are merely different phonetic representations of the same Chinese words.
The desire to cultivate chi led to the evolution of three great traditions of chi kung: medical, spiritual and martial art. Medical chi kung promotes health and well being and is the most commonly known. Spiritual chi kung endeavors to develop the chi in order to access higher esoteric planes of the Self. Martial art chi kung focuses on mastering the dynamics of chi as a means of self-defense.
Nei Kung is a little known system of martial art chi kung which endeavors to stimulate, accumulate and concentrate an inner storehouse of chi within the individual as a source of deep energy and stamina while at the same time comprehensively integrating and conditioning the structural elements of the physical body. Nei means "internal." Nei Kung translates as "internal training", but due to its purpose, principles and practice it is euphemistically referred to as "internal chi kung."