The mucous membranes (or mucosae; singular mucosa) are skin-like linings. They are covered in epithelium. They do secretion, and in the alimentary canal they also do absorption. They line cavities that are exposed to the external environment and internal organs.
At several places they connect up (are contiguous) with the skin. For example, 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 "mucous". The term mucous membrane refers to where they are found in the body. However, not every mucous membrane secretes mucous.