expositional

/ˌɛkspəˈzɪʃənəl/
adjective
  1. Relating to or serving as an exposition; explanatory or descriptive.
    • The novel's expositional chapters set the stage for the main conflict.
    • Her speech was mostly expositional, laying out the facts before the debate began.
    • The documentary's expositional segments helped viewers understand complex scientific ideas.