Prologue - the opening section of a longer work. It also means the preface or introductory part of a novel, long poem, or play.
The term is from the Greek prologos formed by pro, meaning “before,” and logos, meaning “speech.”
In ancient Greek tragedy, the prologue was the part of a play that set forth the subject of the drama before the chorus entered. Prologues were common in the Seventeenth and Eighteenth Centuries, usually in verse—except for plays, when a chorus was used.
The most famous example of a prologue in English is Chaucer’s “General Prologue” in The Canterbury Tales. In this, Chaucer provides a background and setting for what is to follow as well as detailed sketches of the characters.