Trailers: Theatrical Vs Teaser

Theatrical trailers mostly feature clips from the film and give an outline of the film's story-line. They are usually created during the editing of the film, therefore they are likely to contain shots which aren't in the final film. They also often contain music which doesn't appear on the soundtrack or in the film as the composer isn't required until towards the end of the film making process. The purpose of a theatrical trailer is to attract an audience, which is why the most exciting, dramatic, etc, clips are chosen to feature in them. Spoilers must be avoided so the plot or conclusion of the film isn't revealed. For this reason, the scenes are not necessarily in the order in which they appear in the film. The MPAA (Motion Picture Association of America) has given trailers a maximum of 2 and a half minutes to achieve this. Editors and distributors may feel it's necessary to exceed this limit in a particular film, they are allowed to do so once a year. 
Teaser trailers are usually shorter in length (between 30-60 seconds), and contain less footage fro the actual film. They also don't generally contain much information about the film itself or the story-line. They are normally released long in advance of the film they advertise. This is where the name 'teaser' came from as they are designed to 'tease' the audience, as they will have to wait a long time after seeing it to be able to watch the film.
To conclude, teaser trailers are released very far in advance, followed by theatrical trailer when the film is being edited. Due to the film being incomplete, both may contain clips and music which doesn't appear in the actual film. They are designed to tease and attract an audience to view the film when it is released into cinemas.