Differences between teaser and theatrical trailers.

I think the most obvious difference is the length of each one, most teaser trailers are quite short and show fast cuts of the movie, not really including much dialogue or information about what the movie is (hence the word teaser).
Teasers can give the audience the genre of the movie, and a general idea of what it's about. They give enough information to make the audience want to see it, and sometimes the lack of information can make them want to see it more.

Theatrical trailers tend to be longer, show more characters, more dialogue etc. They can also include intertitles to give more information about the movie. I tend to find that when I watch a theatrical trailer, I decide then and there whether or not I'm interested in seeing it, whereas I'll research a teaser trailer as they get me more interested.