A centenarian is a person who has reached the age of 100 years. Because life expectancies worldwide are below 100, the term is invariably associated with longevity. The United Nations in 2012 estimated that there were 316,600 living centenarians worldwide.

Longevity may refer to especially long-lived members of a population, whereas life expectancy is defined statistically as the average number of years remaining at a given age. For example, a population's life expectancy at birth is the same as the average age at death for all people born in the same year.