mucous membrane

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A membrane lining all body passages that communicate with the air, such as the respiratory and alimentary tracts, and having cells and associated glands that secrete mucus.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun anatomy A membrane which secretes mucus. It forms the lining of various body passages that communicate with the air, such as the respiratory, genitourinary, and alimentary tracts including the mouth, nasal passages, vagina and urethra.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun mucus-secreting membrane lining all body cavities or passages that communicate with the exterior