Expectro Patronum, or the Patronus Charm, is a defensive spell which invokes a spirit-like incarnation of the caster's positive emotions. This is used to defend against dark creatures and to send messages to witches and wizards. The image of the caster's Patronus can change when he has gone through a period of heightened emotion. Patronus is Latin for "protector" and, in archaic Latin, "father." Expecto also came from a Latin word which means "I await."