A condition that causes a person to live forever, or in some cases to be incapable of dying
Immortality is a condition that causes the bearer to live forever, or in some cases makes them incapable of dying. In ancient mythologies it was strongly associated with divinity such that while not all immortals were gods and not all gods were immortal in one or sense or the other, most immortals were deities and most deities were immortal.
Some mythology and fiction deals with magic that can make a person immortal, and other stories describe technology that can accomplish similar feats. In biology, there are some primitive organisms that may literally be immortal in the sense that barring violence they can live indefinite lifespans.