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A "bunch" is commonly used to describe a number of flowers. "A bunch of flowers". It can also be used to describe a large number or group of something.

A "flock" normally refers to a group of birds.

A "swarm" is usually referring to some large unregulated group. Commonly insects, such as a swarm of locusts.

For the last one I think you mean "crowd", which normally refers to a large group of people.