Monster Girls are a special type of humanoid where the anthropomorphic character is a mix between a creature (both real and fictional) and a human. Which means some body parts/limbs of a creature has generally been added or switched on a human body. Most of them are an human torso on the top of a monster bottom body. One of the general rule is to keep the face and torso area human. The human is usually a female, though some rare male examples exist.

The umbrella terminology of monster girl can include certain types of personifications of monsters from video games, movies, books and so forth, like vampires, trolls, succubus...
Mythological creatures such as fox girls or other types of humanoid creatures are often included and so forth.

Fetishism involving around monster girls is referred to as teraphilia.