1. In mammals, the membrane that separates the outer ear from the middle ear. It vibrates in response to sound waves and transmits these vibrations via the ear ossicles of the middle ear to the site of hearing (the cochlea of the inner ear). In amphibians and some reptiles there is no external ear and the tympanum is exposed at the skin surface.

2. In insects, an analogous structure that forms part of the tympanal organ, used for detecting sound. Paired tympanal organs can occur at one of various locations on the insect body, including the thorax, abdomen, or legs, depending on species. The tympanum lies on the body surface stretched over an enlarged air channel (trachea) and is associated with sensory hair cells, which detect vibrations of the tympanum and send nerve impulses to the central nervous system.