Earth Prime

Notable characters	Superboy-Prime Legion of Super-Heroes (2004 team), Ultra
First appearance	The Flash #179 (May, 1968)
Publisher	DC Comics

Earth Prime (or Earth-Prime) is a term sometimes used in works of speculative fiction, most notably in DC Comics, involving parallel universes or a multiverse, and refers either to the universe containing "our" Earth, or to a parallel world with a bare minimum of divergence points from Earth as we know it-often the absence or near-absence of metahumans, or with their existence confined to fictional narratives like comics. The "Earth Prime" of a given fictional setting may or may not have an intrinsic value to or vital connection to the other Earths it exists alongside (although it appears to be the case that such Prime Earths -and sometimes the 'central universes' in which those Prime Earths exist as well -are portrayed in fiction to be vital to the existence of the other Earths).

In the DC Multiverse, Earth-Prime is the true Earth from which all the other worlds within the multiverse originate, the actual reality where the readers live, DC Comics operates as a publisher, and all superheroes are fictional. However, Earth Prime became an alternate reality in its first appearance in The Flash #179 (May, 1968), when the Flash accidentally travels there from Earth-One by being pushed by a creature called The Nok. The Flash, stranded, contacts DC Comics editor Julius Schwartz, who helps him construct a cosmic treadmill to return to Earth-One. Eventually it was stated that the writers of DC Comics of Earth Prime subconsciously base their stories on the adventures of the heroes on Earth-One and Earth-Two.

In The Flash #228 (July/Aug 1974), Earth Prime's Cary Bates travels to Earth-One, where he discovers that the stories he writes are not only based on events on Earth-One, but can actually influence these events as well. This power turns for the worse in Justice League of America #123 (October 1975), when Bates is accidentally transported to Earth-Two. The interdimensional trip temporarily turns Bates into a supervillain, and he quickly kills the Justice Society of America. Luckily fellow DC writer Elliot S. Maggin, with the help of the Justice League and the Spectre, is able to restore matters on both Earths in Justice League of America #124 (November 1975).

...
Wikipedia