Trailers are advertisements or promotional movie clips for upcoming movies, but they are shown before the feature film not after, so it seems the name doesn’t make any sense. One would think a better term would be “previews.” As is the case with many English words and phrases, the etymology reflects the history of a specific set of circumstance of when the word was first coined, and although the circumstance changed over time, the word was, in essence, frozen in time. The first trailer was shown after the film The Pleasure Seekers at the Winter Garden Theatre, part of the Marcus Loew theater chain, in New York in November 1913.
The Oxford English Dictionary traces the first use of the term to 1928, but a tireless reseacher from The Straight Dope found a mention as early as 1917, in a New York Times article: ” A committee of the National Association of the Motion Picture Industry yesterday began sending films known as trailers to all of the 15,000 or more movie theatres in the United States. These films are seventy feet in length and will be attached to longer films that are shown at every performance.” Thus, this early mention clearly explains the source of the term: a trailer, a short promotional clip, trails the feature film since it is spliced to the end of the real.
Lexicographer David Wilton notes that trailers served a very important function in the early days of film. In the early days of cinema, theaters would screen several movies in a continuous loop; customers could walk in at any time and stay as long as they wanted. The trailer helped theater owners increase customer turnover, by letting the patrons know when a film ended.
Over the years, the way films were shown evolved, to promote only the feature film. In this context, the trailer would be more effective shown to a captive sitting audience rather than a distracted audience making their way to the exits. In an interview with the Los Angeles Times, Lou Harris, a Paramount executive, mentioned that the industry did try to introduce new terms for the trailer, given the new sequence. Terms like “previews” or “prevues of coming attractions” were introduced, but the old term simply stuck.
Sharp-eyed moviegoers will often notice that certain scenes and music shown in trailers is not in the actual movie. This is due to the fact that trailers are produced far in advance of the film’s completion; the companies that produce trailers use the most compelling footage that is available at the time. Since the soundtrack is the last element added to a film, the trailer production companies use existing music that captures the essence of the film — popular music, scores of other movies, or specially-created “trailer” music. Generally this music never makes it on the soundtrack album, to the disappointment of some movie fans.
The Motion Picture Association of America (MPAA) limits a trailer to 2.5 minutes and rates each trailer: the rating card with the green background is for all audiences and the one with red background is for mature audiences. For trailers on DVDs or the internet, there are no time restrictions.
For further reading: Strike the Baby and Kill the Blonde: An Insider’s Guide to Film Slang by Dave Knox, Three Rivers Press (2005)