Large groups of people gathered together in the same place, or to gather or push closely around something.
From Old English 'crudan' meaning to push or crush. The word originally described the physical action of pressing together, which naturally refers to what crowds do.
Crowds behave so differently from individuals that psychologists call it 'crowd psychology'—a single person might be kind, but put them in a huge crowd and anonymity can make them act in ways they'd never act alone, which is why mobs have done terrible things throughout history.
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