What is a teaser trailer?

Definition from wikipedia -

"A teaser trailer, or teaser is a short trailer used to advertise an upcoming movie, game or television series.

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. They are usually released long in advance of the film they advertise. One of the reasons for the name "teaser" is because they are shown usually a long time (one or one and a half years) before the movie comes out, so as to "tease" the audience."

http://www.wisegeek.com/what-is-a-teaser-trailer.htm

"A teaser trailer is a short version of a movie trailer which is designed to pique the interest of the audience, getting them excited about an upcoming film. Teasers, as they are called, are typically released months in advance, sometimes as much as 18 months before the expected release date of the film, and they are used to build anticipation and curiosity about the films they advertise. Teaser trailers can be seen before feature films in some movie theaters, and they are also released online and shown on television.

Classically, a teaser trailer lasts between half a minute and a minute. It may include footage from the film, often in a rough stage, since the film has not been completed, or it may utilize entirely new source material. In some cases, a teaser trailer is simply an abridged version of a regular movie trailer, including the film's tagline and key footage in a condensed version which is more television-friendly."