The "Grey Zone" is for morally-ambiguous individuals and organizations. They can be Anti-Heroes, Anti-Villains or both, and even Antagonists. Those characters often appear in mature and dark-oriented stories in which the traditionnal "good vs. evil" scenario does not occur.

Their exact nature is debatable, and therefore impossible to truly determine, and it is up for the readers or viewers to make their judgment: while some can see them as heroes, even if they do not approve their methods, some will see them as criminal or even villains (such as V); they can also as well be defined as neutral characters who do not attend to do good nor evil but can be sporadically "heroes" (as Saul Goodman, the Heavy from Team Fortress 2 or Steve from Minecraft).

On & Off characters who commit at the same time heroic and villainous deeds, such as some incarnations of Deadpool, Rick Sanchez or Michael Afton, or false heroes known as "Heroes by proxy" (like many GTA protagonists, such as Trevor Philips) also belong to this category.

Their co-alignment par excellence is Chaotic Neutral, as they almost always follow their own codes and rules (even if they're not heroic). They're rarely Lawful Good, though rare exemples exists (as L Lawliet).

HIGHLY IMPORTANT: heroes whose are Pure Good can never be in this category for they remain good whereas it is unknown if Grey Zones are bad or good.

Also, note that Redeemed Villains are not in the Grey Zone, no matter how bad they were, if they turned Pure Good.

Do not confuse the Grey Zone with On & Off characters, as the latter aren't always evil when they're off but rather misguided (i.e. uninformed, like Papyrus).