Albor Tholus is an extinct volcano in the volcanic province Elysium on Mars. It lies south of the neighbouring volcanoes Elysium Mons and Hecates Tholus. Albor Tholus is 4.5 kilometres high and has a diameter of 160 km at its base. Its caldera has a diameter of 30 km and is 3 km deep, it can put in a whole Mount Etna. (wikipedia entry)
A tholus is a small domical mountain or hill. On Mars they are named after the nearest named albedo feature on the Schiaparelli or Antoniadi maps.