A trailer is an advertisement for an upcoming film that is shown in cinemas. There are two types of trailers: teaser trailers which are 40-60 seconds and give viewers information about the genre, director, and release date. Full trailers are longer and focus more on the plot. Trailers were originally shown at the end of films but now play before movies start to entice audiences to watch featured films. The purpose of trailers is to make viewers want to see the movie by giving a brief sense of the plot, genre, and starring actors without revealing too much.