serous membrane

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

• noun A thin membrane lining a closed body cavity and moistened with a serous fluid.

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

• noun anatomy A thin membrane that secretes serum lining an internal body cavity, such as the peritoneum, the pericardium, and the pleura.

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

• noun a thin membrane lining the closed cavities of the body; has two layers with a space between that is filled with serous fluid