Morgûl

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") remeined within Arda herself.

Magicians who ndraw upon the Mordo are known as Black Magicians, Sorcerers, Black Witches and similar terms.The secret knowledge how to gain power from the Mordo is known as Morgûl (S."Black Knowledge") or Guldur ("Sorcery") or Black or Shadow Magic.