"A Teaser is exactly what it's called..It's main purpose is to just tease the audience. They're usually around a minute (give or take a few) and have minimal visuals, dialogues lines without giving away too much of the movie. Teasers work well to build up anticipation. Trailers are more fleshed out. They have a story line, or a message to communicate. They're longer..around 2 - 2 1/2 mins long (approx). They'll have more dialogues and sometimes narration to reveal more story of the movie. Teaser and Trailers will mix and match footage / dialogue from diff. parts of the movie where as a preview clip..can be an actual scene of the movie exactly the way it is in the movie." Source: Kuldeep Shah, quora