The Third Great Schism represents one of a series of conflicts within the Jedi Order, specifically the third instance, that took place in 4250 BBY. During this schism, certain members of the Order succumbed to the allure of the dark side of the Force and initiated warfare against their Jedi brethren. This particular schism was sparked by Jedi who had been swayed by the dark teachings propagated by the Sith.
Following significant combat on Coruscant, the capital of the Galactic Republic, the Dark Jedi were compelled to retreat to the Vultar system. Within this system, they unearthed ancient technology thought to have been employed in the artificial creation of the planets comprising the star system. The Dark Jedi then tried to operate these machines, one of which was the powerful Cosmic Turbine, but they were unable to maintain control, which led to the destruction of the Vultar system in an event known as the Vultar Cataclysm.
After the devastating cataclysm, the remnants of the destroyed system became known as the Vultar Nebula. The Jedi Order later connected the Third Great Schism to the origins of the Great Sith War, the Jedi Civil War, and the subsequent conflicts between the Jedi and those who had fallen to the dark side.