The Patronus Charm (Expecto Patronum) is the most famous and one of the most powerful defensive charms known to wizardkind. It’s an immensely complicated, very difficult spell that evokes a partially-tangible positive energy force known as a Patronus (pl. Patronuses) or spirit guardian. It is the primary protection against Dementors and Lethifolds, to which there is no other protection.
“Harry was speeding toward the ground when the crowd saw him clap his hand to his mouth as though he was going to be sick-he hit the field on all fours-coughed-and something gold fell into his hand. 'I've got the snitch!' he shouted, waving it above his head, and the game ended in complete confusion. 'He didn't catch it, he nearly swallowed it,' Flint was still howling twenty minutes later, but it made no difference-Harry hadn't broken any rules and Lee Jordan was still happily shouting the results-Griffindor had won by 170 points to 60.”