Comics can be complicated. There are an infinite number of universes in the DC Multiverse "Orrery of Worlds," with a core of 52 worlds in the "local universe." With over a half-dozen more worlds in the Dark Multiverse, that's 60 known worlds in the Multiversity. It can be difficult to keep track of what Earth is what, so we've put together this list of the key inhabitants of each DC Comics Multiverse Earth and what defines it from all the other Earths.
Back in the original DC's Multiverse there were well over a hundred Earths and parallel universes, each with its own version of DC Comics' familiar heroes. Want a Superman who was raised by apes instead of Ma and Pa Kent? Pre-Crisis Earth-183 is for you. With so many worlds and so many storylines, it was a little overwhelming to know what was canon.
In 2007 they tried cleaning things up and streamlined all the places in the old, pre-Crisis storyline down to 52 Earths (with a couple of spots like Limbo and the Antimatter Universe thrown in for good measure). Things still weren't as tidy as they'd like (even though it was still more organized than Marvel's universes) and in 2011, with help from Flash and the always volatile speedforce, DC created the New 52 from Flashpoint, an event that basically destroyed and remade all the universes. It even let them have canon versions of other publisher's properties, like the Marvel Comics on Earth-7 and Earth-8 and Stan Lee's Just Imagine... miniseries on Earth-6.
It does seem like DC is finally satisfied with their current array of Earths, even though the Arrowverse uses it's own slightly different collection of universes.