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A teaser campaign is an advertising campaign which typically consists of a series of small, cryptic, challenging advertisements that anticipate a larger, full-blown campaign for a product launch or otherwise important event. These advertisements are called "teasers" or "teaser ads". A teaser trailer for an upcoming film, television program, video game or similar, is usually released long in advance of the product, so as to "tease" the audience.
For movies 
Movie teasers are usually only made for big-budget and popularly themed movies. Their purpose is less to tell the audience about a movie's content than simply to let them know that the movie is coming up in the near future, and to add to the hype of the upcoming release. Teaser trailers are often made while the film is still in production or being edited and as a result they may feature scenes or alternate versions of scenes that are not in the finished film. Often they contain no dialogue and some (notably Pixar films) have scenes made for use in the trailer only. Teaser trailers today are increasingly focused on internet downloading and the fan convention circuit. Some teaser trailers show a quick montage of scenes from the film.
The teaser for the Batman film starring Michael Keaton was an emergency marketing move that successfully convinced angered comic book fans that the film would respect the source material.
Recent examples of major motion picture events that used teaser trailers to gain hype are the Lord of the Rings trilogy, the Disney/Pixar film Cars, the newer Star Wars films and the Spider-Man films. The Da Vinci Code teaser trailer was released even before a single frame of the movie had been shot. Harry Potter and the Half-Blood Prince's teaser trailer was released surprisingly late, but when it was pushed back from November 21, 2008 to July 17, 2009, the trailer was surprisingly early. Some teasers have appeared over a year (or longer) prior to the movie's release date. For example, a teaser for The Incredibles was attached to the May 2003 film Finding Nemo, a full 18 months before The Incredibles was released. A trailer for Despicable Me 2 was attached to the March 2012 film The Lorax, a full 16 months before its scheduled release. Sometimes a movie goes through so many revisions that there is a long delay between trailer and release. For instance, Where the Wild Things Are had a teaser with How the Grinch Stole Christmas in 2000 but was not released until 2009. It was the longest such gap in history.
A teaser for Star Wars Episode I: The Phantom Menace was attached to the films The Siege and A Bug's Life, and it was reported that many people had paid for admission to the film just to watch the trailer, and had walked out after the trailer had been screened. Teasers for Star Wars Episode II: Attack of the Clones and Star Wars Episode III: Revenge of the Sith were shown before the Pixar films Monsters, Inc. and The Incredibles, respectively. The teaser trailer for Cloverfield was first publicly shown attached to the film Transformers. At this point, nothing about the film was known, and the one-and-a-half-minute teaser did not include the movie title; only the producer's name, J. J. Abrams and a release date, 1.18.08, were shown. The teaser trailer for another film directed by Abrams, Star Trek, was attached to Cloverfield itself, depicting the starship USS Enterprise being constructed on Earth, and again showing no title, the Starfleet Insignia was shown instead. Some teasers that don't show the title but viewers can see the title when the URL for the film's website is shown, such as Battle: Los Angeles. Some URLs don't feature the film's title.
Many DVD versions of movies will have both their teaser and theatrical trailers. One of the more notable exceptions to this rule is Spider-Man, whose teaser trailer featured a mini-movie plot of bank robbers escaping in a helicopter, getting caught from behind and propelled backward into what at first appears to be a net, then is shown to be a gigantic spider web spun between the two towers at the World Trade Center. After the 9/11 attacks, the trailer and associated teaser poster (where the two towers appear as a reflection in Spider-Man's eyepieces) were pulled from distribution in theaters and have never been released on DVD.