Some musings:
I always thought a gray Jedi was someone like Qui-Gon, a maverick who is part of the Order but does his or her own thing for most part. A heretic in a sense.
I never thought of gray Jedi as a non-Jedi Force user, or former Jedi. An ex-Jedi simply is no longer a Jedi since they're no longer part of the Order.
And i definitively never used the term for someone who tries to "balance" good and evil, because that is nonsense as a concept. Using the Dark Side safely is not possible, it is inherently corrupting.
And likewise, the term "dark Jedi" is a misnomer, for dark Jedi are not Jedi. Even if they were Jedi, they aren't exactly Jedi since they've fallen to the Dark Side (well, they might be technically part of the Order so the term would be appropriate in these cases but they're rare to non-existent in practice).
"Force user" is slightly awkward term but more accurate than most others. Usable if a person doesn't belong to an order of some kind and there's no title that could be used. Also, a Force user must be Force sensitive but not all Force sensitives are Force users.
Speaking of balance, to me it seems that balance is a "natural" course with no "personification" of evil like Palpatine or Sith in general. And before someone notes it is odd how two Sith even when the Jedi Order exists is "imbalance", i'll note that the universe is not a thing of symmetry. For example, there's no anti-matter around even though matter and anti-matter are supposedly created equally. Or how certain physical phenomena aren't symmetric (
https://en.wikipedia.org/wiki/Wu_experiment). Of course, it isn't that simple with people like Snoke existing while Palps was alive yet supposedly Anakin restored "balance" by killing Palps. Perhaps the Sith specifically were an aberration?
