sich tummeln
to swarm
To be present in large numbers, often moving around lively and chaotically in one place.
Auf dem Marktplatz tummelten sich Hunderte von Menschen.
Hundreds of people were swarming around the marketplace.

to swarm / hurry
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to swarm
To be present in large numbers, often moving around lively and chaotically in one place.
Auf dem Marktplatz tummelten sich Hunderte von Menschen.
Hundreds of people were swarming around the marketplace.

'Tummeln' (to swarm/hurry) is a reflexive verb and is always used with a reflexive pronoun in the accusative: ich tumm(e)le mich, du tummelst dich, er/sie/es tummelt sich, and so on.
Im Sommer tummeln wir uns oft am See.
In summer, we often hang out at the lake.
In the meaning 'sich an einem Ort aufhalten' (to stay/be in a place), a location is often added with a preposition. Typically, people, children, or animals 'tummeln sich' (swarm/gather) in a certain place.
Im Park tummelten sich viele Familien mit ihren Kindern.
Many families with their children were swarming around the park.
The meaning 'sich beeilen' (to hurry) is colloquial and is rarely used today. You find it almost exclusively in the imperative as a command.
Tummel dich, der Bus wartet nicht auf uns!
Hurry up, the bus won't wait for us!
to teem
'sich tummeln' and 'wimmeln von' both describe many people or animals being in one place and moving around actively. 'sich tummeln' emphasizes the lively movement of the individual people or animals more strongly. It often sounds somewhat positive or neutral, for example with children in a square. 'wimmeln von' mainly emphasizes the large number. The place seems full and hard to take in. Learners may confuse the words because both fit crowded places. A practical rule is: people or animals 'tummeln sich' in a place; a place 'wimmelt von' people or animals.

Auf dem Spielplatz tummeln sich am Nachmittag viele Kinder.
In the afternoon, many children are running around on the playground.
Der Markt wimmelte von Touristen und Straßenmusikern.
The market was teeming with tourists and street musicians.