Pranayama does not really mean control of breath, but the control of the universal energy, Prana, that moves the whole universe. Out of prana is evolved all forms of energy, physical or mental. Thus all physical forces like motion, electricity, magnestism and the rest are expressions of Prana. All the biological functions of the body, the functions of nerve currents and the operations of the mind are also aspects of Prana. Thus the sum total of all forces in the universe, mental and physical, when resolved back to their original state, is Prana. The knowledge and control of this Prana is the real meaning of Pranayama.
- Swami Vivekananda
(Excerpts from The Four Yogas of Swami Vivekananda, condensed and retold by Swami Tapasyananda)