There are many definitions of the msyterious chti, the biophysical energy said to be generated by respiratory rhythm. The concept was probably introduced by Mencius (Chinese Medicine, Pierre Huard ante Ming Wong). Ch'i manifests itself in the five elements of the universe to give substance to the world, but flows through the elements in the form of a life energy which, if understood, can be controlled.

Ch'i is everywhere.

It can be seen in one's handwriting or calligraphy. The Chinese calligrapher strove to impart his control over ch'i through his brush to his writing. It might be thought of as a force which gives life, or which holds the moon in place, or which holds an atom to an electron. The concept of ch'i was fundamental to the philosophies of China (Taoism and Buddhism) and, therefore, to its martial arts. Internal systems of kung-fu were very concerned with ch'i-kung (spirit manipulation); the external styles, in contrast, concentrated less on principles of ch'i-kung. (MICHAEL P. STAPLES)
See also further reading: The Secret of the Golden Flower, C.G. Jung, 1962.

See Ki.