A thin layer or fold of tissue, usually supported by a fibrous network, serving to cover or line some part or organ, and often secreting or absorbing certain fluids.
- Biology A thin, pliable layer of tissue covering surfaces or separating or connecting regions, structures, or organs of an animal or a plant.
- Biology Cell membrane.
- A piece of parchment.
- Chemistry A thin sheet of natural or synthetic material that is permeable to substances in solution.