A trailer (also known as a preview or coming attraction) is a commercial advertisement for a feature film that will be exhibited in the future at a cinema, the result of creative and technical work. The term "trailer" dates back to the distribution of movies on reels of film. The reels were always distributed un-rewound (the theater about to show the film first had to rewind it, as early experience showed the danger of expecting an incoming film to have been rewound). Therefore, the end of the movie was the most accessible part, to which previews were spliced, "trailing" the film.
Movie trailers have now become popular on DVDs and Blu-ray discs, as well as on the Internet and mobile devices. Of some 10 billion videos watched online annually, film trailers rank third, after news and user-created video. The trailer format has also been adopted as a promotional tool for television shows, video games, books, and theatrical events/concerts.