A film or movie in which the story-line and/or characters were only supporting roles in a previous theatrical release. It is similar to a
spin-off on television.
Synonym: a side-story of movie
It differs from a sequel in which the story-line and characters are assumed to take place chronologically AFTER the original
work . It also differs from a prequel in which the story-line and characters are assumed to take place chronologically BEFORE the original
work.
An important characteristic of a sidequel is that the film
may not even allude to of any of the principle characters of the original
work. It is usually also retains the same director, writer, etc.
The movie, "This Is 40", is a sidequel of "Knocked Up" since it primarily follows the side story of
Pete (Paul Rudd) and
Debbie (Leslie
Mann), the in-laws of Alison Scott (Katherine Heigl) in the original film.