Found on Wikipedia:
There is an ongoing controversy in metaphysics about whether or not there are, in addition to actual, existing things, non-actual or nonexistent things. [...] Note that "actual" may not mean the same as "existing". Perhaps there exist things that are merely possible, but not actual. (Maybe they exist in other universes, and these universes are other "possible worlds"--possible alternatives to the actual world.) Perhaps some actual things are nonexistent. (Sherlock Holmes seems to be an actual example of a fictional character; one might think there are many other characters Arthur Conan Doyle might have invented, though he actually invented Holmes.)
Existence is reserved for things we have access to. Possible existence implies possible access. Actual existence implies actual access. Non-existence implies no possible access.
It is certainly possible to describe things outside of all possible access. For example as mentioned above we can talk about "non-actual or nonexistent things" and "possible worlds" that we can't access because they are counterfactual or because they are a separate reality. But when we talk about things beyond all possible access, we are just making up stories, a...
If it's worth saying, but not worth its own post, even in Discussion, it goes here.