What do you call a "random person" in a movie? I remember there was a word, in fact, several words for it, but I forgot all of them. For example, Hollywood will pay people to act like a random passerby. What are these called?
Such a person is called an extra (or background actor).
A background actor or extra is a performer in a film, television show, stage, musical, opera or ballet production, who appears in a nonspeaking or nonsinging (silent) capacity, usually in the background (for example, in an audience or busy street scene). War films and epic films often employ background actors in large numbers: some films have featured hundreds or even thousands of paid background actors as cast members (hence the term "cast of thousands").
An older term, still used in theater, is "spear carrier" indicating a person who added to the impression of an army by appearing and carrying a spear as part of a group, but had no lines. "Extra" is now more common. This term is not used in film or TV, as I understand it.
If the person has any lines, the term "minor character" may be used.
Occasionally a very minor part is written for someone connected to the show, such as the producer or director, or for a well known actor not otherwise involved. This is called a "walk-on" because the person just walks on and off, saying little or nothing. Alfred Hitchcock was noted for having walk-ons in many of his productions.