The ability to live beyond a regular human's lifespan.
In most stories, there's at least one way to become immortal whether they are born with it or if they had an strange force inside of them or if they achieved an supernatural goal. Examples range from being bitten by a vampire or werewolf to drinking a strange elixir.
there are some who wish to obtain this goal to live forever and will fight to gain that goal. having immortality is ever humans dream once they are born they never want to die and try to obtain immortality and live beyond that of a normal humans life span but even immortality has its weak points some who are immortal cannot die but there is a weakness to there long life.
there are other ways to obtain immortality some ways many use is to just simple place there souls into anothers body and do the same over and over when the body becomes old and useless the users body may be young but their soul could be thousands of years old due to the body switching.