mana
The energy of life wielded in the forging of intentions (spells). Also known as prana, qi and the like.
As incarnate characters in the mortal plane, we have a limited amount of mana which is our life-force. While it is possible to draw much higher levels of life-force through the body than is commonly perceived, the mortal plane is intrinsically impermanent. Our energies are not limitless.
As the generation point for invocations, mana is the raw source of energy behind our intentions. To accomplish spells, we must be able to utilize mana.
Prana, mana, qi and the like are all synonyms for the sensation of life force.