On the Elemental and Outer Planes

Overview

It has been established that what we call the material plane isn't exactly a whole working piece by itself. Indeed, the complex composition that makes up the material plane is in fact a subtle interweaving of many other "elements", perhaps countless more than we can fathom. They seem to exist as elemental "planes" in their own right -- not necessarily limited to the "classic" four elements of Fire, Water, Air and Earth, though all four appear to be prominent. Theory holds that these elemental "planes", each "two-dimensional" in form, weave together in endless astral knots to form pockets of "three-dimensional" spaces. Though the correct terminology is "Outer Space", colloquially they are still referred to as "Outer Planes" due to an archaic understanding of how planes work.
These weaves are not evenly dispersed throughout the world, and thus different things seem to appear based on the concentration of each plane: oceanic regions often register higher concentrations of the water plane, for instance. As our world changes, so does the "weave" pull and tug in several directions and indeed several dimensions, perhaps more than we can accurately measure with our current scientific instruments. Though Aeyvis is so far the only known world that is overall balanced in its elemental composition, modern academics believe that there are other worlds in a similar state, perhaps an infinite number of such worlds that we have yet to discover.
Through feats of modern design several magical organizations have been able to "tap" into this weave, allowing for planar shift and exploration given that the traveler knows how to tune their instruments of magic to the proper wavelength. As the weave is everywhere, it is possible to shift to another realm from anywhere in the world, as far as most scholars know. In fact, it is through this technology that teleportation was first discovered, by shifting to another plane (in this case, the "astral sea") and immediately coming back to the material plane wavelength. This aptly solves the conundrum that previous scholars had with instant teleportation of what once appeared to be immutable space - though the science of exact calibrations of target locations is still a hot area of study.

On Naming Conventions

There is no strict naming convention for the Outer Planes, as the generally infinite combinations that are possible cannot be realistically constrained to some Gerceni-approved list. Rather, people generally tend to cite the name in the paper that first established the existence of such a plane -- which, tradition holds, is a meaningful adjective of some sort. This naming convention started with the discovery of the Pelagic, as many scholars did not actually know the meaning of the word, and did not grasp onto the fact that the word simply described the plane as an open sea.

On Living in Other Planes

One thing that has especially fascinated researchers is the "livability" of Aeyvis, a "balanced" or "Material" plane, as opposed to the imbalanced Outer Planes we have observed thus far. It has been noted that each plane is in fact its own world, with ecosystems and sentient inhabitants who may not necessarily (and usually don't) follow the same physical rules and laws that those on Aeyvis do. (For instance, many flames burn endlessly in the Igneous despite a lack of oxygen to eat and kindling to burn.)
Pioneers of interplanar travel have found that they have no problem entering these realms, traversing them, or even conversing with their inhabitants -- granted they keep to their own physical laws, such as eating food and breathing. However, natives who have attempted to travel from their planes to our Material Plane find themselves extremely weakened, often succumbing to physical laws within the span of several days. Scholars agree for the most part that this is due to their bodies learning to subsist only on the matter and laws of their native plane, and upon coming to the material plane "lacking" the other parts necessary.
After several scholars of the adventurous type set up extended outposts in various planes and found themselves weak or slightly atrophied after return to the material plane, this theory has been all but confirmed, and most interplanar regulatory committees mandate a minimum of 5/2 work/rest days for scholars travelling to and from such areas.

On Planar Exile

An emerging controversial practice in several magically-inclined nations has been, in order to save space and "be merciful", to permanently exile (nonmagical) life-sentence criminals to life on another plane. So far the practice has been limited to relatively stable planes, such as the Scintillate and the Igneous (surpisingly mild, despite the title).
Philosophers have debated the ethics of a "death penalty" enforced by sending criminals to their certain death, in planes such as the Empyrean (a barely explored area of nothing but air and sky), the Gant (an area of near eternal darkness) or the Luminous (an area seeming to be comprised entirely of blinding, endless light).