A teaser trailer, or just teaser, is a short trailer used to advertise an upcoming film, television program, video game or similar, usually released long in advance of the product, so as to "tease" the audience.
Teasers are also commonly used in advertising. The so-called teaser ad or teaser campaign typically consists of a series of small, cryptic, challenging advertisements which anticipate a larger, full-blown campaign for a product launch or otherwise important event.
Movie teasers, unlike typical theatrical trailers, are usually very short in length (between 30–60 seconds) and usually contain little, if any, actual footage from the film. Sometimes, it is merely a truncated version of a theatrical trailer. Theatrical trailers are previews of upcoming attractions but are much more detailed than a teaser trailer. It may provide plenty of detail to what the plot is about.
Teaser trailers are usually only made for big-budget and popularly themed movies. Their purpose is 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. Other ones (notably Pixar films) have scenes made for use in the trailer only. Teaser trailers today are increasingly focused on internet downloading and the convention circuit.
source: http://en.wikipedia.org/wiki/Teaser_trailer
