Pranayama

Pranayama refers to breathing exercises, specifically as a part of Yoga practice and yogic techniques.  Pranayama literally means "breath control" indicating that as we control or guide our prana - our breath or life force - we can affect our physical and mental state.  Certain pranayama are used to balance and calm the mind and body while others are invigorating or stimulating.   Pranayama is used with the asana practice (yoga postures) and also on its' own to affect the physiological state.

"When the Breath wanders, the mind is unsteady,

but when the Breath is still, so is the mind still."

                                    -Hatha Yoga Pradipika