The difference between a teaser trailer and a theatrical trailer

Theatrical trailers are shown just before the films release on TV and cinemas. They are usually much more longer than teaser trailers. 

Teaser trailers are meant to tease. They do not reveal much of the plot and are supposed to be a minor glimpse of what the film is about. On the other hand a theatrical trailer provides plenty of detail about what the film. There have been many complaints that they give away to much information and ruin the plot of the film. Teaser trailers only reveal the most important clips whereas theatrical trailers contain more clips of the film. Usually teasers starts with an establishing shot setting the scene which is telling us where the action is going to take place.