In the world of BDSM role-play, a mommy is a dominant female figure who acts as another partner's mother. More specifically, it is a type of age play in which a woman pretends to be an older woman taking care of her much younger child. The submissive partners in these relationships are often referred to as "littles." During play, mommies may punish their littles in various ways, such as by spanking, or nurture them, such as by cuddling with them, or a combination of both.
When a male assumes this role, he is referred to as a daddy.
Mommies overlap significantly with mistresses in other types of female dominance, only this type of relationship tends to be gentler and more nurturing, and to avoid dynamics like servitude.