Prana (Sanskrit for "moving force"), the life force, or airs, within the body, divided by Hindu philosophy into ten classifications. The classifications begin with the breath and include the air of digestion, of evacuation, of relaxation, of opening and closing the eyes and mouth, of contraction, of circulation, and of sustenance. The seat of the life airs is the heart. Prana is closely connected with yoga, which includes the idea that calm breathing brings calmness of mind.