Plain English Meaning
A thin layer of tissue inside your ear that picks up sound and also feels changes in air pressure. It separates the outer ear from a small air space behind it, so when the pressure on one side doesn't match the other, the eardrum gets pushed in or out.
Full Definition
A thin, taut membrane at the end of the ear canal that vibrates in response to sound waves and pressure changes, transmitting those vibrations to the small bones of the middle ear. It also forms the boundary between the outer ear and the air-filled middle ear cavity, so any difference in pressure between those two sides pushes the membrane inward or outward.
Context Anchor
Seen in aviation physiology discussions about the ears, especially when explaining pressure changes during climbs and descents and how the ear helps with hearing and balance.