A crowd scene actor, also known as an EXTRA, is someone who appears in the background of a movie or television show. An EXTRA is usually not given any lines and is used to fill out a scene with other actors. A MOB is a large group of people, often used to create a chaotic atmosphere in a scene. Therefore, a crowd scene actor is someone who is part of a large group of people in a movie or television show, often without any lines or speaking roles.