preparty

pre- +‎ party

preparty (plural preparties)

1. A party held before the start of an event, usually a public event.
   • 2008 January 22, David Carr, “Shopping for Films but Settling for Some Fun”, in New York Times‎:

     In true Sundance fashion, there was a preparty for the film, an intimate little dinner that was blown out to include hundreds, followed by the movie itself, and then an afterparty featuring a set by the Honey Brothers, a band that includes both Mr. Grenier and Mr. Gold.

• afterparty