Subfertility is the failure to conceive after 12 months of sexual intercourse without protection or use of contraceptives.

Infertility is the complete inability to conceive.

Monthly Fertility Rate (MFR) is the probability of conception in a menstrual cycle.

The human is not a particularly fertile mammal. It is estimated that in humans the MFR is 20%, while in baboons it is 80% and in rabbits 90%.