Definitions for "Prequel"
a sequel (comes out second) that depicts events happening before the story it is a sequel to
A movie that presents the characters/events chronologically before the setting of a previous film.
A movie that presents the characters and/or events chronologically before the setting of a previously filmed movie. See also series, serial, contrast with sequel.
a post hoc addition to a previous work, not a planned completion of it
a book in a series set at a time prior to the existing titles.
a corporate move to make more money