A mob is a large, disorderly crowd of people, often acting together in a dangerous or violent way. When individuals form a mob, they can lose their individual judgment and get swept up in the group's emotions and actions. History shows many examples of mobs doing terrible things that the same people would never do alone: destroying property, attacking innocent people, or demanding punishment without fair trials.

Mobs are often fickle: they can form quickly, act impulsively, and dissolve just as fast. A peaceful protest can sometimes turn into a mob if people stop thinking for themselves and start following the crowd's worst impulses.

In everyday speech, people use mob more loosely to mean any large, pushy crowd. You might say a mob of shoppers rushed into the store on opening day, or a mob of students crowded around the lunch cart. These uses are less serious but capture the same sense of chaotic group behavior.

The word also refers to organized criminal groups, especially the Mafia. When someone talks about “the mob” in this context, they mean professional criminals working together.