Prequel

Prequel is a term in drama and literature: it is a fusion of the words 'precursor' and 'sequel'. 
When a story is told in several stages, it is natural to tell it in order of time. For example, a series of books on the Second World War started with the 1930s and ended up in 1946. 
For various reasons, this does not always happen. In the movie series "Star Wars", the first movie was ' (1977). It was followed by three prequels, which were ' (1999); ' (2002) and ' (2005).
For correct use, the term 'prequel' is only applied when work is part of a series, and when the later publication refers to an earlier time. It is an old idea, but one which is often used today for drama on movie and television. The "Cypria", a work of Ancient Greek literature, is a prequel to Homer's "Iliad". A related idea is the back-story, which is the background story of a main story or character.