"Expecto Patronum" is a powerful spell from the Harry Potter series, created by author J.K. Rowling. It is used to conjure a Patronus, a protective charm that takes the form of an animal. This spell is particularly effective against Dementors, dark creatures that feed on happiness and can induce despair. To successfully cast "Expecto Patronum," a wizard or witch must focus on a strong, positive memory. The strength of the Patronus depends on the caster's emotional state and the clarity of the memory. Each person's Patronus is unique and often reflects their personality or inner qualities.