Sorry to gang up on you, but that's simply incorrect.denseWorm said:A deus ex machina is tool used by playwrights to summarise plots to the audience and make connections that they might not have seen, in short to 'cheat' a way out of a complex plot. Gandalf plays a deus ex machina when he comes back to Gimli, Aragorn and Legolas in The Two Towers and fills them in on just about everything.
What you're describing here is gratuitous exposition, which is completely different from deus ex machina. The latter does not necessarily involve any summarising, and in some cases is left completely unexplained (i.e. the opposite of what you've described).
In simple terms, a deus ex machina is any resolution to a conflict which hasn't been properly set up beforehand. You could argue that in Star Wars Episode VI, the Death Star having a really convenient weak spot was a deus ex machina. The reason why this weak spot exists is never explained to the audience or even mentioned ever again.