Immortality is the idea that you are not affected by mortality, the ability (if you can really call it that) to die of "natural causes". Many forms of Mythical Undead such as Vampires and Liches. There was a show called Highlander about an Immortal from the Scottish Highlands, who gained power by cutting off the heads of other Immortals. When he did this it was called The Quickening, because in the end, THERE CAN BE ONLY ONE!