Trail•er [trey-ler]

Who knew?

From dictionary.com:

• a short promotional film composed of clips showing highlights of a movie due for release in the near future

And from wikipedia:

• Trailers or previews are film advertisements for feature films that will be exhibited in the future at a cinema, on whose screen they are shown. The term "trailer" comes from their having originally been shown at the end of a feature film screening.
• Trailers consist of a series of selected shots from the film being advertised. Since the purpose of the trailer is to attract an audience to the film, these excerpts are usually drawn from the most exciting, funny, or otherwise noteworthy parts of the film but in abbreviated form and usually without producing spoilers.