The eredar are a species native to Argus. Over time, they have split into several subspecies.
MAN'ARI ❝ UNNATURAL BEINGS ❞ The eredar that sided with Sargeras after Archimonde and Kil'jaeden accepted his bargain. They became twisted by the fel magic they embraced and became demonic beings. Their technical name is "man'ari eredar," though "eredar" has evolved to become virtually synonymous with these demons.
DRAENEI ❝ EXILED ONES ❞ The eredar that rejected Sargeras and followed Velen. They are the race playable in game. They may technically called "draenic eredar" considering their species hasn't changed, while their affiliation has, but the majority seem content with simply calling themselves draenei.
KROKUL ❝ BROKEN ❞ (Draenor)—After the events of Shattrath, some draenei found that they were cut off from the Light, and later, began mutating. They were seen by many as unsettling and to be kept separate from the unaffected draenei. As a result, many banded together while in hiding.
(Argus)—Not every eredar left behind on Argus followed Sargeras. Some took to hiding away in the most remote corners of the world while the Legion made it its primary base of operation. Presumably, as a result of the fel energies seeping into the planet and corrupting it, the renegade eredar mutated into krokul similarly to how their cousins on Draenor had.
LOST ONES Some of the Krokul from Draenor further degraded while surviving out in the wilds. They became known as "Lost Ones," creatures who had lost most if not all of the sanity, and became vicious and violent.
LIGHTFORGED DRAENEI The Lightforged were originally draenei who fled Argus aboard the Genedar, but separated from their brethren aboard the Xenedar. Under the lead of the naaru Xe'ra, they were infused with the Holy Light and went to battle against the Burning Legion as part of the Army of Light.
Following the defeat of the Burning Legion, they aligned themselves with the Alliance and its cause. Additionally, new recruits among Velen's draenei are being sought, and have chosen to undergo the ritual to become Lightforged.