In its most general form, a nipple is a structure from which a fluid emanates. More specifically, it is the projection on the breasts or udder of a mammal by which breast milk is delivered to a mother's young. In this sense, it is often called a teat, especially when referring to non-humans, and the medical term used to refer to it is papilla. The rubber mouthpiece of a baby bottle or pacifier may also be referred to as a "nipple" or a "teat". In many cultures, female nipples are considered an erogenous zone and it is considered a public indecency to uncover them in public.