The eardrum is a thin, tight piece of skin stretched inside your ear, like the skin on a small drum. When sound hits it, it shakes, and that shaking is how hearing starts. You cannot see it from the outside; the flap on the side of your head is not the eardrum. Everyday English says eardrum; a doctor may say tympanic membrane, which is the same thing in clinic language. A very loud bang, a bad ear infection, or a fast change of pressure (a plane, a deep dive) can tear it. It often heals, but it hurts and hearing can drop for a while. Though actually, “that concert burst my eardrums” is often only a joke about volume — but a real blast can do real harm, so the joke sits close to a true warning.