what are teaser trailers?

A teaser trailer, is a short trailer used to advertise an upcoming film, television program, video game, or product. 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 shortened version of a theatrical trailer. They are usually released long in advance of the film they advertise.