I will provide a few takes, this first one comes from Ayurveda The Science of Self-Healing...
"It is vital energy (life-energy) which activates the body and mind. Prana is responsible for the higher cerebral functions, and the motor and sensory activities. The prana located in the head is the vital prana, while prana which is present in the cosmic air is nutrient prana. There is a constant exchange of energy between vital prana and nutrient prana through respiration. During inspiration, the nutrient prana enters the system and nourishes the vital prana. During expiration, subtle waste products are expelled."
Though this term has been familiar to me for some time, a few weeks ago a conversation I had with a friend briefly taught me about the different ways different people may obtain prana. It can come from taking a very cold shower, engaging with other people and receiving prana from relationships; it is in the foods we eat, and the consciousness with which we approach our food (and other facets of our interactive lives), taking a moment to pause before putting fork-to-mouth to express gratitude for the sacrifice (if animal products are consumed) and purity of energy we are about to consume. A friend of mine once gave some lovely advice: to consider the trip taken by the various elements on your plate while you mindfully chew your food (an essential part of the digestive process). From the seed planted in the ground and where the ground is. Then, the care with which that seed was nourished by the sun, the farmer, the rains and temperatures of the air. Imagining the plant growing and finally being harvested, how it was packaged and through what hands it passed (human or machine) to get to the crates and containers, then loaded onto trucks or planes... How much energy was given to deliver the food-energy to your grocer or dining establishment? If you cooked the food yourself, how much thought did you put into the process? Were you conscious of the feel of the knife in your hand and the pressure and sensation of passing this knife through the skin of that plant or animal? Then combining it with other elements, taking care of the heat and flavors as it cooked... The more aware we become of the inter-connectedness and the path of these infinite energies making up our daily lives, the better we are equipped to make the best choices for our selves, for our loved ones and for the communities we live in... all a part of the bigger picture, containing the bigger picture, while being contained by the global... our holographic reality.
Here is another excerpt, from Light on Life (p. 102):
"Consciousness (citta) and vital energy (prana) are in constant association. Where consciousness is focused, there must be the energy of prana too, and where you direct the energy of prana, consciousness follows. Consciousness is propelled by two powerful forces, energy (prana) and desires (vasana). It moves in the direction of whichever force is most powerful. If breath (prana) prevails, then desires are controlled, the senses are held in check and the mind is pacified. If the force of desire gets the upper hand, the breathing becomes uneven, and the mind becomes agitated. These are things you can actually observe, just as you observe right measure and balance in asana (the yoga postures), and this is why and where the practice of yoga brings self-knowledge. You will not reach Knowledge of the Divine Self without passing through self-knowledge. Your practice is your laboratory, and your methods must become ever more penetrating and sophisticated. Whether you are in asana or doing pranayama (conscious breathing), the awareness of the body extends outward, but the senses of perception, mind, and intelligence should be drawn inward"...
And from good 'ol Wiki:
Prana (प्राण, prāṇa) is the Sanskrit for "vital life" (from the root prā "to fill", cognate to Latin plenus "full"). It is one of the five organs of vitality or sensation:
viz. prana "breath"
and manas "thought" (nose, mouth, eyes, ears and mind).
In Vedantic philosophy, prana is the notion of a vital, life-sustaining force of living beings and vital energy, comparable to the Chinese notion of Qi. Prana is a central concept in Ayurveda and Yoga where it is believed to flow through a network of fine subtle channels called nadis. Its most subtle material form is the breath, but it is also to be found in the blood, and its most concentrated form is semen in men and vaginal fluid in women.
In Ayurveda, the Prana is further classified into subcategories, referred to as prana vayus. According to Hindu philosophy these are the vital principles of basic energy and subtle faculties of an individual that sustain physiological processes. There are five pranas or vital currents in the Hindu system:
- Prana : Responsible for the beating of the heart and breathing. Prana enters the body through the breath and is sent to every cell through the circulatory system.
- Apana : Responsible for the elimination of waste products from the body through the lungs and excretory systems.
- Udana : Responsible for producing sounds through the vocal apparatus, as in speaking, singing, laughing, and crying. Also it represents the conscious energy required to produce the vocal sounds corresponding to the intent of the being. Hence Samyama on udana gives the higher centers total control over the body.
- Samana : Responsible for the digestion of food and cell metabolism (i.e. the repair and manufacture of new cells and growth). Samana also includes the heat regulating processes of the body. Auras are projections of this current. By meditational practices one can see auras of light around every being. Yogis who do special practise on samana can produce a blazing aura at will.
- Vyana : Responsible for the expansion and contraction processes of the body, e.g. the voluntary muscular system.