A rabble is a noisy gathering of people. The police might arrive to calm the rabble that crowds the sidewalks after a huge win for the local football team.
You can use the noun rabble for any mob of angry or excited people, whether it's a political gathering or a rowdy celebration. Rabble also means "commoners," but it's a snobby and somewhat offensive way to talk about ordinary folks: "The king preferred to stay inside his castle, far away from the rabble." Originally, rabble meant "pack of animals."