A technical question:

What is the exact definition of a teaser in Tv series? From what I have been reading on these boards it is a relatively short scene that comes before the main titles. If that's the case what is the term used for this same type of segment when it occurs immediately after the main titles as in Gilligan's Island's first 2 seasons or in the Brady Bunch? I would call these prologues. Also what do you call the trailer like bits taken from an upcoming episode of a show (usually this was done with a lot of the dramas of the 70s and 80s) that come just before the main titles? I can't think of any show that uses this device now but some older shows may have had an actor or announcer preface these clips with "Tonight on..."

Technical question #2:

To me the term tag suggests an ending scene that is kind of extraneous to the plot of a show (in other words a syndicate could lop off the tag and viewers wouldn't really miss any of the central plot). Yet there are a few sitcoms where the plot's resolution doesn't occur until this "tag" scene. Get Smart in the 60s had an entire season of these types of episodes where you had to watch all the way through to the very end to see how the conflict was resolved. On Roseanne, Dan's heart attack and the family winning the lotto occur in these "tag" scenes which ran under the closing credits. People who tuned out the closing credits of Roseanne missed 2 of the most significant plot points in that series' history.

So what is a tag and what would you call it when the plot is resolved in that brief 1-3 minute segment at the end of a show?

All I can say is, don't change the channel of your favorite show until the next show begins. (that's the only way you'll know its over)

What's odd with Roseanne though is that the credits start about five minutes before the episode ends.
Then it goes to commercial.... and comes back and doesnt continue the credits until half way through that.

I'm pretty sure the opening scene before the theme song/opening credits is called the teaser, and the final scene, during the closing credits, is the tag scene. That's how it's defined on scripts I've seen, anyway.

Yep the teaser is what opens up the episode, just a short scene then usually the credits, or some shows they open with the credits then go to the teaser.

The tag scene is the very last scene of the episode, it basically sums up what happened in the episode :)

Teasers are also sometimes referred to as "cold opens".

I've noticed that Roseanne doesn't even wrap up the story until the tag- sometimes the tag runs 4 or 5 minutes.