exposition

Definition (noun): a systematic interpretation or explanation (usually written) of a specific topic

Definition (noun): a collection of things (goods or works of art etc.) for public display

Definition (noun): an account that sets forth the meaning or intent of a writing or discourse

Example: we would have understood the play better if there had been some initial exposition of the background

Definition (noun): (music) the section of a movement (especially in sonata form) where the major musical themes first occur