Mommy is a biological and/or social female parent of an offspring. In the case of a mammal such as a human, the biological mother gestates a fertilized ovum, which is called first an embryo, and then a fetus. This gestation occurs in the mother's uterus from conception until the fetus is sufficiently developed to be born. The mother then goes into labor and gives birth. Once the child is born, the mother produces milk in a process called lactation to feed the child; often the mother's breast milk is the child's sole nourishment for the first year or more of the child's life.

The title mommy is often given to a woman other than biological parent, if it is she who fulfills the social role. This is most commonly either an adoptive mother or a stepmother. Currently, with advances in reproductive technologies, the function of biological motherhood can be split between the genetic mother and the gestational mother, and in theory neither might be the social mother.