What is distinctive about differences between trailers and teaser trailers?

Trailers are usually longer than teaser trailers with trailers being 2 to 3 minutes whereas a teaser trailer will only last about 1 and a half mins. The teaser trailer will advertise short shots of the film that give very little away, only a small amount of the narrative so the audience are attracted to the film but dont know too much about it.
Teaser trailers are often distributed before the full length trailer because they announce the film is coming and give the target audience a taster of the film, which they will later find more about in the trailer. Full length trailers are screened shortly before the film opens which may follow on from a teaser trailer which is shown in advance, not all films decide to have teaser trailers, the distributors and production company will discuss whether they want one or not.
Both trailers and teasers have to be effective at giving the audience glimpses of the film through a number of edited shots from the film, the making of a trailer takes work, and these trailers become very popular both online, TV, Cinema, and even on DVDS so the thought that goes into the trailer is important whereas the teaser would probably be shown for a shorter period of time when the film is coming out in a more distant future than what a trailer would show.