trilogy

A trilogy is three related things put together. It could be books, movies, or even songs that tell a story.

You might hear someone talk about a trilogy because it's common for authors to write three connected novels or filmmakers to make three sequels to a popular movie. A good example of this would be the "Lord of the Rings" series by J.R.R. Tolkien – you have the book, and then two others that follow what happens next. Sometimes TV shows do trilogies too; they'll have a pilot episode followed by two more. When someone says their favorite movie is part of a trilogy, it means there are three parts to the story, all connected in some way.