Virginal membrane: A thin membrane which completely or partially occludes the vaginal opening. This fold of mucous membrane is usually present at birth at the orifice of the vagina. In medicine, it is called the vaginal membrane or the hymen. Hymen is a Greek word meaning "skin" or "membrane." The ancient Greeks applied the word "hymen" to all kinds of membranes including, for example, the membrane that surrounds the heart (the pericardium). Starting in the 1500s the word was restricted to refer only to the vaginal membrane.