A big magical stone that has been mystically linked into the every living being of the world of Midkemia. If its powers would be used, all life would disappear from Midkemia. The stone was created by the Valheru (by Alma-Lodaka, unless I remember incorrectly).

"Tomas turned his attention to the Lifestone, an artifact he knew in some ways more intimately than any living being on Midkemia. He let his mind relax and watched the cool green surface, and after a moment saw a pulsing light, faint and hard to apprehend if one tried too hard." - Raymond E. Feist: Rage of the Demon King