2) An ending that leaves elements unresolved, allowing for sequels or just to shit people.
3) The usual way the second part of a trilogy ends, seeing as how most trilogies are not planned as trilogies, but seeing as how well the first did, producers and other money grabbers decide adding two more movies, books, etc. So when the time comes for an ending to the second part (seeing as how most sequels are never as good as the original) they need to give you a reason to come back for the third part.
2) "that was such an unending! What about all those zombies? and how did they get there in the first place!?!?!"
3) Examples include: Matrix trilogy, Pirates of the Caribbean triolgy, Halo Triolgy, etc etc