curtain-raiser
noun
[ ˈkəːt(ə)nˌreɪzə ]
• an entertainment or other event happening just before a longer or more important one.
• "Bach's Sinfonia in B flat was an ideal curtain-raiser to Mozart's last piano concerto"
Origin:
late 19th century: originally used in the theatre to denote a short opening piece performed before a play.
