An understudy is a theatrical term for someone who learns the lines and moves of a leading actor or actress in a theatrical play. Should the lead actor or actress be unable to appear on stage because of illness or accident, the understudy takes over the part. Usually, when the understudy takes over, the theater manager will make the anouncement prior to the start of the performance. Several actors made their name in showbiz by being the understudy of a leading actor and taking the role over for several performances.