Prana means life force or vital energy. Is it derived from etymology pra+anna, where 'pra' means before and 'anna' means food or physical matter. Thus prana is the state of matter before it becomes physical. It can be understood as the liquid state of matter before matter solidifies and becomes physical matter. Prana should not be confused with physical energy such as light, heat or radiation because they too are forms of physical matter. Rather prana is what precedes any kind of physical matter altogether. The prana is said to not reside in the physical plane of reality, but reside in the [wiki]akasha[/wiki] or the ether just beyond the physical plane. Here all matter exists as waves or vibrations.
The classical texts ennumerate 5 types of prana as per their function in the body: udana, upwards flowing life force which deals with speech generation and exhalation; apana, downwards flowing life force which deals with inhalation; samana, the life force that deals with metabolism; vyana, the life force that deals with circulation in the body and finally prana itself; the major life force which is coordinating them all.
In classical Yoga as dictated in the [wiki]Yoga sutras[/wiki] the control of prana or pranayama is the fourth limb of Yoga. The prana is traditionally controlled through the regulation of breath, but in Kriya yoga the prana can also be controlled through mechnical yogic exercises or kriyas. In the Yogic tradition a special branch of Yoga science is called Prana Vidya, literally science of prana, where the yogis learns to master all movements of prana in the body and outside of the body and transmit and receive prana at will.
In the Yoga sutras many of the supernormal abilities described in the third chapter rely on control of prana. For example levitation happens when one attains perfect control of the udana vayu or upwards flowing prana. The yogi may at will cause his/her body to rise by manipulating this prana.