Gray Jedi are by definition Force-users who “walk the path between the light and dark [sides] without surrendering to either.”Gray Jedi did use some strong dark side powers: force-lightening, force-choke, etc. The reason they were not considered Sith is that while they openly wielded the dark side, they were not corrupted by it.

The Jedi Council’s prophecy states that the “Chosen One will bring balance to the Force by destroying the Sith.” The prophecy was fulfilled, BUT:
how is destroying the Dark Side bringing balance? This is why I lost my faith in the Jedi.

As for Sith, they feed off the darkest emotions there are: they combine their opponent’s fear with their own anger to forge hate, the weapon of the dark side. I mean, really, who could do that all their life? Yeah, besides the Emperor; he does a pretty good job of it.

The solution to the problem is the Gray Jedi. The keep the balance–actual balance–between the Jedi and Sith.

Gray Jedi make their way into both the Jedi Order and the Dark Council, as well as their own society, helping whichever side they believe needs help the most. In this way, they ensure the survival of both sides, but don’t allow either to destroy the other.

Some groups of Gray Jedi: The Voss Mystics, a force-sensetive species of the planet Voss, who allied themselves with neither party; Jensaarai, an order of Force users from the Suarbi System who considered themselves neither good nor evil; and Imperial Knights, who have nothing to do with the Sith Empire: they are their own, separate, non-dark side Empire from years after the fall of the more commonly known Empire. Jolee Bindo (human male), was also a self proclaimed Gray Jedi. Qui-Gon Jinn and Mace Windu were also suspected to be Gray, but neither case was proven.