PRANAYAMA IS DERIVED fron two Sanskrit words - prana (life) and ayama (control). Pranayama is therefore life control and not "breath control." The broadest meaning of the word prana is force of energy. In this sense, the universe is filled with prana; all creation is a manifestation of force, a play of force. Everything that was, is, or shall be, is nothing but the different modes of expression of the universal force. The universal prana is thus the Para-Prakiti (pure Nature), immanent energy or force which is derived from the infinite Spirit, and which permeates and sustains the universe.
Source: God Talks with Arjuna: The Bhagavad Gita, Pages: Volume 1, 497
Contributed by: David