I know that "opening number" is the more common term, but I was wondering if there exists a technical term known only by composers.

Specifically, I'm thinking about the kind of opening number that foreshadows all the music that will be performed later throughout the musical. For example, Jesus Christ Superstar: the opening number was basically a medley of the story's highlights.

Is there a special term for that kind of piece? If so, I imagine it would be an Italian expression.