Eyelid: The lid or cover of the eye, a movable fold of skin and muscle that can be closed over the eyeball or opened at will. Each eye has an upper and a lower lid. Also known as a palpebra. SLIDESHOW Pink Eye (Conjunctivitis) Symptoms, Causes, Treatments See Slideshow From Eye Health Resources Eye Care When You Have Graves' Eye DiseaseFinding the Care You Need for MS Featured Centers Good and Bad Foods for PsoriasisVideo: Getting Personal on Life With MS Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19