A reality is the collection of a universe where a version of the planet Earth exists and shares space and time with the corresponding celestial bodies (an Earthspace), and the various other dimensions associated with it, like Asgard, the Dark Dimension or the Negative Zone, to name a few. Universes where a planet Earth exists are infinite, and there is (generally) one version of Asgard, one version of the Dark Dimension, one version of the Negative Zone, and so on, associated with each.^[1]

Most stories take place on Earth, so this planet is arbitrarily regarded as the nucleus of the reality it belongs to. Because of this, the term "Earth" is often used interchangeably with "reality," specifically in regards to the concept of alternate realities. In a similar context, the term "universe" is also used to refer to a reality, since the Earth is contained within a universe-type of dimension.

Realities are categorized using a numbering system, with each reality being assigned a unique number. The most correct term to designate a reality is "Reality-XXXX" (with the unique numeration of a given reality replacing "XXXX"). However, due to the aforementioned placement of the Earth as the centerpiece of any given reality, reality designations commonly use the prefix "Earth-" instead, thus "Reality-616" is colloquially known as Earth-616.^[1]