All of those people you see wandering around the background of your favorite movies and television shows are called "extras." Extras are actors and actresses who serve as "dressed background." They help to sell the idea that a scene is filled with real people just going about their daily business.

Extras aren't always professional actors. In fact, most extras are just regular folk who wanted to be a part of the film and television industry. Extras are paid a fairly small wage for their participation and they are usually expected to stay on set from the beginning of production until wrap (the end of production).SAG-signatory producers are allowed to hire non-union background actors after a certain number of SAG performers have been cast; non-union background actors are usually paid the minimum wage. On productions outside of union jurisdiction, payment for background actors is at the discretion of the producers, and ranges from union-scale rates to "copy and credit" (i.e., no pay). Those producers who do not pay their actors may be in violation of state and federal laws about minimum wage for a job.
Between 1946 and 1992, background actors in film and television were largely represented by the Screen Extras Guild. SEG was disbanded on 1 June 1992 and transferred its jurisdiction to SAG

Depending on the type, size and budget of the production, the extras may or may not take part in makeup, wardrobe, hair, etc. Often many period pieces will entail that the extras are "fully dressed and fitted" which means that they are provided with costuming by the wardrobe department. But more often than not, extras are simply informed beforehand of the type of clothing they will need to bring and asked to furnish it themselves.