From what I read, this is a plot device whereby a divine or unforeseen force resolves all the the MC's problems. Shakespeare used it in some of his plays, the Greeks made heavy use of it. One essay I read said it's fine to use it to get the MC into an issue, but not out of it. That's fine. However, the question I have is what's the delineating line between deus ex machina and something that was there all the time, but just hanging out of sight? My screenplay uses what I probably would consider deus ex machina to get the MC in deep and change his life forever, but it's something that was there for 70 some odd years waiting.