Apparition, it is used for a Witch or Wizard, to get somewhere they want to go, in a matter of seconds. Apparating is a very useful spell, for alot of Witches and wizards.
Dumbledore and Harry Disapperated from Hogwarts when going to the cave to retrieve a Horcrux.
Mundungus panicked and Disapparated when Voldemort came at him.
Hermione recommended Disapparating and heading for the countryside from Tottenham Court Road.