Dis (Dite) is the prison city of Dante’s Inferno, presumably in circle 6 or 7, or on the border between circles. It lies between circle 6 (Hecate) and circle 7 and beyond (violence, fraud, treachery).
It is an infernal fortress with prisons, whether for souls or for subjugated demons is unclear. Entities such as Hecate guard it, and it can be taken or negotiated.
It is a critical geographic point of the infernal journey: controlling it gives the group access to the lower circles or an exit to the upper world.
It is probably the same city mentioned in earlier episodes. The name confirms the Dantesque source, since “Dite” is a synonym of Dis, or hell, in Dante’s Inferno.