21 hours in and whoa there is a very involved discussion going on. So I'm going to answer the original question instead.
@il-volpe asked:
What exactly is one, in your learned opinion?
The events of the greater world which go far in defining that world and much that happens within it. Some people might call that "setting", but the setting is simply where the events take place.
For instance, in one world, "winter is coming" is a meta-plot. It is an event that will be happening, but it's an event so large that it influences even small events within it, such as the event of, "better chop some more wood, then, and by wood I mean kill all Starks."
In another world, it might be "God is in a coma". The movie is not at all about God being in a coma, but the movie happens because of that over-arching condition of the world.