prologue
opening to a story that establishes the setting and gives background details or introductory scene, monologue preceding a play, or an introduction to a work, including musical work, or story in general
en-US/ˈpɹoʊlɑɡ/
en-GB/ˈpɹəʊlɒɡ/
opening to a story that establishes the setting and gives background details or introductory scene, monologue preceding a play, or an introduction to a work, including musical work, or story in general