Story structure
Epigraph
A phrase, quotation or poem set at the beginning of a book, chapter or section to preface or frame it.
In literature, an epigraph is "a phrase, quotation, or poem that is set at the beginning of a document, monograph," section or chapter; a book may carry one epigraph, one per chapter, or both. Its uses, as the article lists them: "as a preface to the work; as a summary; as a counter-example," or as a link to the wider canon that invites comparison. T. S. Eliot set Dante over "The Love Song of J. Alfred Prufrock," and Cormac McCarthy opened Blood Meridian with three epigraphs.
Fiction also forges them: the article files Fitzgerald's D'Invilliers poem in The Great Gatsby and Tolkien's Ring Verse under fictional epigraphs, story artifacts doing epigraph work. For serial writers the epigraph is a cheap, load-bearing hook: three lines at a chapter's head can set tone, prime the theme and signal register before any scene starts. It stands beside the prologue as the other before-the-story page.