Maximum life span (or, for humans, maximum reported age at death) is a measure of the maximum amount of time one or more members of a population have been observed to survive between birth and death. The term can also denote an estimate of the maximum amount of time that a member of a given species could survive between birth and death, provided circumstances that are optimal to that member's longevity.
Most living species have an upper limit on the number of times somatic cells not expressing telomerase can divide. This is called the Hayflick limit, although this number of cell divisions does not strictly control lifespan.