Trailers vs teaser trailers:

Teaser trailers are usually released a year to a year and a half before the film itself is released. They are short trailers (between 30 and 60 seconds) that promote an upcoming movie. Unlike actual movie trailers, teasers often don't use much of the film footage, if any. Teasers use small, cryptic challenges to literaly tease and/or intregue an audience. By using teaser trailers an audience is slowly built up with anticipation to see the movie; they create a buzz within audiences who will talk up the teasers and ultimaty the film itself.

Movie trailers on the other hand are much more direct, giving much more information to the audience (title, genre, characters, bits of story-line etc.) but still enough to entice the viewer to go and see the film.