Rancora is a fel-infused Burning Legion world. It is a landscape of festering pools and skittering death, and many skittering demons originate from it. Portal Keeper Hasabel opens a portal to Rancora during her encounter in Antorus, the Burning Throne, summoning the aranasi Lady Dacidion and Feltouched Skitterer spider demons.
Based on its description and the demons who come through the portal, Rancora may be the aranasi's homeworld. Hasabel's description of it fits with what is seen of aranasi territories, so at the very least they are a prominent presence on it.