A Prequel
- (narratology) In a series of works, an installment that is set chronologically before its predecessor, especially the original narrative or (perhaps improper usage) any narrative work with at least one sequel. Prequel - Wikipedia
Usage notes
Most often used, not as a direct antonym of sequel, to refer to earlier works in a series, but to refer to works that are chronologically before but are created and released after; an archetypal example is the *Star Wars* prequel trilogy.