SpellsCharm
Expecto Patronum
Expecto Patronum is the incantation of the Patronus Charm. It calls a guardian of positive feeling that drives off Dementors. Remus Lupin teaches it to Harry in private lessons after the Hogwarts Express attack. Harry’s Patronus takes the form of a stag.
First mention
Harry Potter and the Prisoner of AzkabanChapter: The Patronus
Lupin sets a Boggart that becomes a Dementor and has Harry practice the incantation.