What is the meaning of exposition?

noun

• A systematic interpretation or explanation (usually written) of a specific topic.
  • synonyms: expounding
• A collection of things (goods or works of art etc.) for public display.
  • synonyms: exhibition, expo
• An account that sets forth the meaning or intent of a writing or discourse.
  • usage: "we would have understood the play better if there had been some initial exposition of the background"
• Music) the section of a movement (especially in sonata form) where the major musical themes first occur. (.