Demographic transition: This term describes the historical shift from high birth and death rates to low birth and death rates that many countries experience as they develop.
Fertility rate: The fertility rate refers to the average number of children that would be born to a woman during her lifetime based on current age-specific fertility rates.
Replacement level fertility: Replacement level fertility is the number of children each woman needs to have on average for a population to replace itself without migration, typically around 2.1 children per woman.