Before Morgoth was banished from Arda he had started to "melt" himself with the World.After his fall this Morgoth-Element, known as the Mordo ("Stain, Shadow, Grotesque") remained within Arda herself. Magicians who drew upon the Mordo were known as Black Magicians, Dark or Shadow Mages,evil Sorcerers, Black Witches and similar terms.The secret knowledge how to gain power from the Mordo was known as Morgûl (S."Black Knowledge") or Guldur ("Sorcery"), Felu ("Evil") or Black or Shadow Magic.