What A Teaser Trailer?

A teaser trailer is a short version of a normal movie trailer which is designed to intrigue and interest the audience. Teasers on the other hand are typically released months in advance, sometimes even as much as 18 months before the release of the film, they are used to build curiosity about the film and to get people talking about it. A teaser trailer normally lasts around 30-60 seconds, it may include footage from the film but they often use rough footage since the film has not normally been completed around teaser trailer stage. Sometimes a teaser trailer is an abridged version of a regular movie trailer, just with a little more mystery. Teaser trailers are usually only made for big budget and popular movies, their purpose isn’t to tell the audience about the movie's content but more to let them know that the movie is coming up in the near future, and to add to the hype of the upcoming release. Some big companies I have noticed like to make teasers that literally tease their audiences, for example, a teaser trailer might flash a few key images, followed by a title card with the date. 
This works best for iconic films and films in a series, as viewers become familiar with specific symbols. A good example of this type of teaser trailer would be the promotion of the Batman films, which flashed the famous Batman symbol on the screen, followed by a date. The brief advertisement of a teaser trailer is usually not terribly costly to make or expensive to air on television or cinema screens, and it easily sucks viewers in, getting people hyped up about a movie months before it is released is a great advertising bonus.