The mucous membranes (or mucosae; singular mucosa) are skin-like linings of mostly endodermal origin. They are covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs. They are at several places contiguous with skin: at the nostrils, the mouth, the lips, the eyelids, the ears, the genital area, and the anus. Unlike skin which has hair growing out of it, mucous membranes are hairless.
The sticky, thick fluid secreted by the mucous membranes and glands is called "mucus". The term mucous membrane refers to where they are found in the body and not every mucous membrane secretes mucus.