Muma Pădurii literally means "the Mother of the Forest", though "mumă" is an archaic version of "mamă" (mother), which has a fairy-tale overtone for the Romanian reader (somewhat analogue to using the archaic pronouns like "thou" and "thy" in English). A few other such words, typically protagonists of folk-tales, have this effect.
Muma Pădurii is a spirit of the forest in a very ugly and old woman's body. Sometimes she has the ability to change her shape. She lives in a dark, dreadful, hidden little house. This (step-) mother of the forest kidnaps little children and enslaves them. In one of the popular stories, at some point, she tries to boil a little girl, alive, in a soup. However the little girl's brother outsmarts Muma Pădurii and pushes the woman-monster in the oven instead, similar to the story of Hansel and Gretel. The story ends on a happy note when all kids are free to go back to their parents. Instead of saying "she's ugly", Romanians sometimes say "she looks like muma pădurii".
She is thought to attack children, and because of this, a large variety of spells (descântece in Romanian) are used against her.