Most television series have a "regular cast" or "main cast". These are the actors who are regularly on the show each week. They are commonly called just "regulars" or "main characters". Programs will often need other actors to play smaller roles in the series. These are called "guest stars". A guest star may only be used for a single episode or they may be used for more than one. This often happens if the character's story goes on for more than one episode. Often, a character will be used for many episodes, but over a long period of time not for episodes shown one after the other. These are called "recurring characters" and are characters that are not "regulars", they are not part of the main cast, but are used many times during the series.