Prāṇa

Prāṇa (प्राण) is the Sanskrit word for "vital life" (from the root prā). In Vedantic philosophy, prana is the notion of a vital, life-sustaining force of living beings and vital energy, comparable to the Chinese notion of Qi. In human beings, it flows through a network of fine subtle channels called nāḍis.

In the Theosophical literature prāṇa is the third (sometimes second) principle of human beings, usually referred as "life principle" or "vital principle."

In Theosophy

Mme. Blavatsky defines prāṇa as follows:

"Prana," or "Life," is, strictly speaking, the radiating force or Energy of Atma -- as the Universal Life and the ONE SELF, -- ITS lower or rather (in its effects) more physical, because manifesting, aspect. Prana or Life permeates the whole being of the objective Universe; and is called a "principle" only because it is an indispensable factor and the deus ex machina of the living man.