A covering flap in animals, such as a gill cover.
A gum flap covering (part of) a partially erupted tooth, usually a wisdom tooth.
The lidlike portion of a moss sporangium or of a fruit that detaches to allow the dispersal of spores or seeds.
One of several flaps of cerebral cortex covering the insula.
A structure which serves as a cover or lid.
The blowhole of a whale, dolphin or other similar species.
A pore or opening used (especially by arthropods and some fish) for respiration.
Any small aperture or vent for air or other fluid.