From Statistics Explained
Fertility is the ability to conceive (become pregnant) and give birth to children.
The total fertility rate is defined as the mean number of children who would be born to a woman during her lifetime, if she were to spend her childbearing years conforming to the age-specific fertility rates, that have been measured in a given year.
The age-specific fertility rate or the fertility rate by age of mother is the number of births to mothers of age x proportional to the average female population of age x.
- Fertility (ESMS metadata file - demo_fer_esms)