The reproductive performance of an individual, a couple, a group, or a population.

The term fertility is used instead of birth rate when births are counted in relation to the number of women of reproductive age. The fertility of a cohort can be summarized by completed fertility and mean age at childbearing, whereas the total fertility rate (TFR) measures the fertility of a given year. When a distinction is made by birth order, the terms first-birth fertility, second-birth fertility etc. are used.