Difference between a trailer and a teaser trailer

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. Tester trailers 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