What term describes a phenomenon where the average age of a population increases over time?

The term that describes the phenomenon in which the average age of a population increases over time is "Aging Population." This occurs when higher life expectancy, lower birth rates, and sometimes decreasing mortality rates lead to a shift in the demographic structure, resulting in a larger proportion of older individuals compared to younger ones. An aging population can have significant implications for a society, including increased demand for healthcare services, potential labor shortages, and challenges related to pensions and social services.

Understanding this term is crucial in analyzing demographic trends and their impacts on various socio-economic factors. In contrast, terms like "Population Growth" refer to an increase in the total number of individuals in a population without a specific focus on age, "Population Decline" indicates a decrease in population size, and "Demographic Transition" is a model used to explain the transition from high birth and death rates to lower birth and death rates as a country develops, which may include an aging aspect, but is not solely defined by it.