The number of offspring produced by a female organism. In a population, biological fertility is measured as the general fertility rate (the birth rate multiplied by the number of sexually productive females) or as the total fertility rate (the lifetime average number of offspring per female). General dictionaries list fertility and fecundity as synonyms for reproductive fruitfulness. In population biology, biological fertility refers to the number of offspring actually produced, while fecundity is merely the biological ability to reproduce. Fecund individuals that fail to mate do not produce offspring (that is, are not biologically fertile), and do not contribute to population growth.