Xoroth

Xoroth is one of the fiery, chaotic worlds belonging to the Burning Legion, or more specifically, the Nathrezim, or Dreadlords. This is home to the infernal Dreadsteeds, mounts to the Dreadlords. They are owned by Lord Hel'nurath, the "stable keeper". Players will have to summon a Dreadsteed in a quest for a warlock's epic mount by opening a portal to this world in Dire Maul.

Dreadsteeds roam the fiery Plains of Xoroth.

Inhabitants of this world summoned to Dire Maul include Xorothian Dreadsteeds, Xorothian Imps, and Dread Guards.

Xorothian Eredar, Xorothian Satyr and Xorothian Imps are among the creatures emerging from portals from other worlds within Mazthoril.

Speculation
Given that Xoroth is the home of the Dreadsteeds, it is possible that Xoroth is the world where the Dreadlords established their citadel (seen in The Dreadlords Convene, an interlude from the Undead campaign in Reign of Chaos). However, given the number of worlds consumed by the Legion, the Citadel could reside on another Nathrezim world, or even on Argus.

It is possible that the Tothrezim also inhabit this world.

When fought in Onslaught Harbor, Mal'Ganis yells "Enough! I waste my time. I must gather my strength on the homeworld." This, and the Artifact from the Nathrezim Homeworld dropped by Mal'Ganis for hints that the Nathrezim homeworld, be it Xoroth or not, may have a role to play in the future.

In, Varimathras has a "Master" on the far side of a portal represented as "A distant voice". This may be related the Nathrezim homeworld.