prelusion
/ˈpriːljʊˌzən/Definitions
1. noun
A musical introduction, especially one for a symphony; a prelude.
“The orchestra’s prelusion to the main concert was a beautiful rendition of Bach’s Toccata and Fugue in D minor.”
2. noun
An introductory section or passage, especially one that serves as a warning or an explanation.
“The prelusion to the main plot of the story was a detailed description of the characters’ backgrounds.”