"The formula for immortality is the greatest secret in the universe. I know this to be true because I have been alive for more than seventeen centuries." -- author unknown.
Immortality is a state of being that is possessed by only a few entities, though others may claim it to a degree. Immortal beings either do not age, or age to such a slow degree that it has become imperceptible. They also may possess abilities that render them immune to death or resistance to injury.