Teasers and Theatrical Trailers

The difference I see between teasers and theatrical trailers is that teasers tend to be shorter, revealing less of the plot and leaving the viewer with an idea of what's to come but plenty of questions. Theatrical trailers come later and are usually longer, giving away more of the plot but again leaving the audience with questions in their mind.

I also find that the way teasers are edited is often confusing, especially in the context of a horror, with scenes out of the order they would appear in, and sometimes a quick pace between the scenes to give a feeling of anticipation.