Dark Jedi

Dark Jedi were force sensitive individuals who chose to deny the light side of the Force or follow the dark side, though did not follow the teachings of the Sith. Although "Dark Jedi" originally referred to a Jedi who had fallen to the dark side, it could also refer to uninitiated Force-sensitives who received no Jedi training but began their careers under another Dark Jedi.

The term "Dark Jedi" was used by the Sith as a catch-all term for a Dark-Sided Force User who wasn't a Sith Lord, to denote the difference between the Sith teachings and the mere act of using the Dark Side of the Force.

Noteworthy Dark Jedi
The most notorious and noteworthy Dark Jedi was Supreme Leader Snoke, who gathered the Imperial Remnant and formed the First Order in an attempt to reconquer the Galaxy. His apprentice, Kylo Ren, and the other Knights of Ren were also known colloqially as Dark Jedi.

Rey Beniko, the last of the actual Jedi Order, was also a prominent Dark Jedi and the first instance of a Dark Jedi leading the Jedi Order. Her Dark Sided tendencies were a result of her being trained by Darth Amorosa in the wake of Luke Skywalker's uncooperative approach to Jedi training.