Board Thread:News and Announcements/@comment-5047768-20131003005753/@comment-4651179-20131003014534

Basically, both DC and Marvel somehow "incorrectly" give universes the definition of "Earths".

So, when in comics is being talked about an Earth or Earths, it's being talked about an universe or universes. So when it's not about our green and blue planet, "Earth" is an expression used to refer to an universe/reality.

So, an entire universe (not only the planet Earth) is an Earth. Our entire universe is called Earth-1218 in the Marvel fiction, as an example.

And based on the theory that multiple universes exist, there are numerous Earths in the multiverse.

So numbers is the way to differentiate different Earths. The Marvel Universe (the universe where the mainstream Marvel stories are set) is called Earth-616, while the Marvel Cinematic Universe (the universe where all Avengers-related movies takes place) is Earth-199999, and so on.