rumhängen
to hang around
Informal for spending time idly or without a specific goal, often together with others.
Die Jugendlichen hängen nach der Schule oft im Park rum.
After school, the teenagers often hang around in the park.

to hang around
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to hang around
Informal for spending time idly or without a specific goal, often together with others.
Die Jugendlichen hängen nach der Schule oft im Park rum.
After school, the teenagers often hang around in the park.

'Rumhängen' is the colloquial short form of the separable verb 'herumhängen' (to hang around / hang down). The prefix 'rum-' always signals informal, spoken usage.
Was habt ihr am Wochenende gemacht? – Nicht viel, wir haben nur zu Hause rumgehangen.
What did you do on the weekend? — Not much, we just hung around at home.
As a separable verb, the prefix 'rum' stands at the end in a main clause. In a subordinate clause or in the infinitive with 'zu', the verb stays together.
Er hängt oft mit seinen Freunden im Einkaufszentrum rum.
He often hangs around at the mall with his friends.
You can recognize the meaning from the subject: When a person 'rumhängt', they spend time idly. When an object or body part 'rumhängt', it hangs down limply or messily.
Die Teenager hängen jeden Nachmittag im Park rum.
The teenagers hang around in the park every afternoon.
When people 'rumhängen' (hang around), it often happens in certain places or with certain people. Typical combinations are 'mit Freunden rumhängen' (to hang around with friends), 'im Park rumhängen' (to hang around in the park), or 'zu Hause rumhängen' (to hang around at home).
Lass uns heute Abend nicht ausgehen, sondern einfach bei mir rumhängen und einen Film schauen.
Let's not go out tonight, but just hang around at my place and watch a movie.
to hang
'hängen' and 'rumhängen' can both describe something hanging downward. 'hängen' is neutral and only says that something is attached at one point and hangs freely downward. 'rumhängen' sounds colloquial and often somewhat negative: something is hanging down limply, messily, or unattractively. In addition, 'rumhängen' can mean spending time without a goal. That is exactly why it can be confusing. For a coat on a coat rack, you would normally say 'hängen'. For teenagers with no plan in the park, or for a loose cable, 'rumhängen' fits better.

Nach der Schule hängen die Jugendlichen oft noch eine Stunde am Bahnhof rum.
After school, the teenagers often hang around at the station for another hour.
Das Bild hängt seit gestern über dem Sofa.
The picture has been hanging above the sofa since yesterday.