"Metaphenomenal," a word which one can find tossed off on various websites but has no entry under the Onelook Dictionaries, is in all likelihood a neologism that various people have tossed out for various reasons.
My independent invention of the term (at least as I remember coining it) was a take on Kant's famous distinction between the "noumenal" and the "phenomenal," where "phenomenal" indicates everything that can be identified through its physical presence and "noumenal" as everything that cannot.
This struck me as being broadly applicable to the situation within a fictive universe. Some fictive universes depict only representations of what our culture calls its consensual reality; the things that a majority agrees on as being real. Other fictive universes depict things that may never exist, or which do not yet exist, and this requires the author to describe such things largely from imagination rather than experience as such. This struck as me as a loose parallel to Kant's "noumenality" in some ways but not in others, so I discarded his term and substituted one for purely literary purposes: "the metaphenomenal," meaning "beyond the phenomenal." I consider it a better catch-all for all things that owe their existence to mankind's imagination than the usual catch-all employed in academic studies: "the fantastic." There's both logic and tradition to using the latter term, yet it seems at times cumbersome when dealing with phenomenon that go beyond phenomenal limits within a given universe, and yet are not supposed to be regarded as "fantastic" within that universe even though they may be to the majority of readers. "Metaphenomenal," to my mind, efficiently takes in both the viewpoints of readers and of the characters designed for the story as to whether a given element is within the sphere of ordinary phenomena or not.
In my next post I'll be using my chosen term on occasion, so this is essentially a quick-and-dirty explanation of said term for the purpose of the upcoming essay.