Fecundity, coming from the word fecund, generally means the ability to reproduce.
In biology and demography, fecundity is the ability to reproduce of an organism or population, measured by the number of gametes (eggs), seed set or asexual propagules. Fecundity is under both genetic and environmental control, and is the major measure of biological fitness. Fecundation is another term for fertilisation.
Fecundity can increase or decrease in a population according to current conditions and certain regulating factors. For instance, in times of hardship for a population such as a lack of food, juvenile and eventually adult fecundity may decrease.