The Golden Snitch (or just Snitch) is one of the four balls used in the wizarding sport of quidditch, a game introduced in the Harry Potter book series by J.K. Rowling. Capturing the Snitch is worth 150 points, and a game of quidditch can only end when the Snitch is caught.
The Snitch is enchanted to avoid Quidditch players on both teams. It is a small ball that is around walnut-sized according to the books, and flies on small, silver wings. Each quidditch team has a Seeker, the one player whose only job is to find and capture the Snitch. The other players include three Chasers who try to score the Quaffle through the hoop at either end of the pitch (for 10 points), two Beaters who attempt to smack the 2-iron Bludger balls towards their opponents while protecting their own teammates, and a Keeper in front of each hoop where the quaffle is scored. These players largely ignore the Golden Snitch. The only player allowed to capture the Snitch is the Seeker on either team. Consequentially, Seekers spend most of the quidditch match away from the action, looking for and chasing the Snitch.
Harry Potter is the Seeker for the Gryffindor quidditch team, and he often successfully captures the Snitch to end matches. In Harry Potter and the Deathly Hallows, the importance of the Golden Snitch is more than sporting or symbolic, as Harry finds that Dumbledore had left him the first Snitch he had ever caught, inside of which was the Resurrection Stone.
Quidditch has also been adopted to muggle life with some alterations to account for the lack of magic. In this version, the Snitch is often a person who runs around to avoid the Seekers on either team. Variations where the Snitch is a tennis ball in a sock tied to the runner have also been used.