Soul

Every creature has a soul, which acts as the container for all magical energy, and as a glue that keeps the physical body stable. Souls are something the universe cannot create so they must be recycled by the Void. Souls will get dumped into the Void roughly 10 minutes after the body dies, though those with more amplitude for magic can stay around a bit longer, and a soul can be bound to a new body to give the Soul more time.

Magic Well

The Soul is where a person's arcane energy resides, this well of energy is where most spells will default to when collecting the energy needed for a spell. Some forms of magic might require other things (See Gilrin for an example), these will use their sources of energy to pay the cost. But the most common way is the Well of Mana creatures have. For more info about Magic see Magic.

A Soul Without a Body

Souls can live outside a body for some time. On Average its 10 minutes before the soul is dumped into the Void, this timer is a bit more fuzzy is the soul is Void Immune. In most cases this will happen when the body dies, but there is other ways it can happen such as having the soul removed via magic.

Some people will willingly remove their souls from their body as a way to scout around or maybe to project it elsewhere in the world. In most cases this is a short term spell, since they can only do this for 10 minutes before the universe kicks them out. Some casters have found ways around this requirement, either by latching onto nearby bodies, or creating a link between their soul and body letting them stay out longer.