Life Force is one of the two forms of mystical energies that practitioners of both arcane and divine magic meld with the other form of energy, Dream Force, to cast their spells.
Life Force is naturally produced by every living thing on earth, from the slightest blade of grass to the largest leviathans. Practitioners of both arcane magic and divine magic “see” strands of this energy and snatch threads of it to weave their magic.
Life Force is not naturally produced in the Outer Planes. While a small amount seeps across the Veil to the Outer Planes, the most powerful deities in the Outer Planes receive Life Force projected to them through the prayers of worshippers.
Undead creatures in Adnati do not produce Life Force, but still depend on it for survival. They are drawn to this energy in living creatures and prey on them for the Life Force power in their blood, their brains, and their flesh.