Longevity

The word "longevity" is sometimes used as a synonym for "life expectancy" in demography - especially when it concerns someone or something lasting longer than expected (an ancient tree, for example) - however, the two words have slightly different definitions. In a similar dichotomy to "precision" and "accuracy", "longevity" refers to the average number of years that a single person lives, whereas "life expectancy" refers to the number of years that the average population lives. This is illustrated by the fact that a drastic increase in life expectancy (due to a larger portion of the population beginning to live longer) may be accompanied by a small increase in the overall longevity of the population.

Reflections on longevity have usually gone beyond acknowledging the brevity of human life and have included thinking about methods to extend life. Longevity has been a topic not only for the scientific community but also for writers of travel, science fiction, and utopian novels.

There are many difficulties in authenticating the longest human life span ever by modern verification standards, owing to inaccurate or incomplete birth statistics. Fiction, legend, and folklore have proposed or claimed life spans in the past or future vastly longer than those verified by modern standards, and longevity narratives and unverified longevity claims frequently speak of their existence in the present.

A life annuity is a form of longevity insurance.