Comic fans and companies have a jargon that is used all the time, even in comic book titles, that new fans may find confusing. A “Comic Code.” Let’s look at one of the terms…
Earth One (also Earth-1 or Earth 1) is a term used in the DC Universe (and in discussions of it) to identify a parallel universe. It is also (especially prior to 2011) used as a descriptor too differentiate between versions of a character. (The Earth-1 Superman, for example). The term is usually applied to universes containing Silver Age DC Universe or versions of them.
1. The Silver Age Universe – When, during the Silver Age of Comics, DC reintroduced the Golden Age characters as coming from a parallel universe called Earth-Two and thus named the new Silver Age universe Earth-One.
2. The Evil Universe – After Crisis on Infinite Earths, other universes merged into mainline universe Earth-One, because of the changes this Universe was no longer named Earth-One. Grant Morrison’s 2000 comic JLA: Earth 2, introduced a new parallel universe (resembling the one traditionally called Earth-Three), which the inhabitants called Earth 1.
3. One of the 52 Earths – After the Infinite Crisis event, one of the new Earths, many people assumed that the mainline universe was called Earth-1 again, however, it was called “New Earth” and instead new comics were produced under the title of Earth One, those being the Original Graphic Novels Superman: Earth One and Batman: Earth One.