curtain-raiser

In a theater, an initial play, musical performance, etc., which precedes the main performance.

[H]e had tried all kinds: comedy, tragedy, prose and verse, the light curtain-raiser, the short sharp drama, the bourgeoisrealistic and the lyrical-romantic.

“Capricious Maneuvers,” the eight-minute romp of a curtain raiser that Mr. Peck made for City Ballet’s 2013 Fall Gala, was fun.

A prelude or introduction to an activity or thing.

It is my opinion that your part in the affair is only a curtain-raiser to graver things.

But the first foray by Russian strategic bombers into the Western hemisphere since the Cold War is simply the curtain raiser for joint naval maneuvers that will bring Russian warships into Venezuelan waters in November.