Definition of Button, from a Broadway Glossary:
Button: The payoff moment in a song; the moment when the song is “buttoned up” and finished.
On Broadway, music composers know that nearly all of the time, they need to deliver a button on their songs…. that point in the music when the audience knows the song is over, and it’s time to applaud. The same concept applies when editing music for performance dance routines. When a song fades out, your audience is robbed of the routine’s button. That’s why Squirrel Trench Audio retains the ending of the original song so that the button is delivered to your dancer. The audience knows the routine is over and it’s time to clap.
There are times when a song might have a big musical finish that lasts 20 seconds or more. These type of endings, while great in a music performance, are too long for a dance performance. In such cases, we will edit down the big finish into an appropriate length for the dance routine.