rund
round
Having the shape of a circle or a sphere.
Der Tisch in der Küche ist rund.
The table in the kitchen is round.

round / about
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round
Having the shape of a circle or a sphere.
Der Tisch in der Küche ist rund.
The table in the kitchen is round.

The word 'rund' (round/about) has two very different main functions: it can describe a shape or indicate an approximate amount. The context, especially whether a number follows, makes the difference clear.
Wir saßen an einem runden Tisch.
We sat at a round table.
When 'rund' (about) means 'ungefähr' (approximately), it stands directly before a number and is not declined. It behaves like an adverb.
Die Wanderung dauert rund drei Stunden.
The hike takes about three hours.
In the figurative meaning 'stimmig' (coherent) or 'abgeschlossen' (complete), 'rund' (well-rounded) is often used in phrases like 'eine runde Sache' (a well-rounded thing/a success) or 'ein runder Abschluss' (a fitting conclusion).
Dank der guten Organisation war das Fest eine runde Sache.
Thanks to the good organization, the festival was a well-rounded success.
The expression 'rund um' (all about/around) + accusative means 'everything that has to do with a topic.' It is often used in the service and information sectors.
Die Messe bietet Informationen rund um das Haus.
The trade fair offers information on all matters related to the home.
The idiom 'rund um die Uhr' (around the clock) is a fixed unit and means '24 hours a day, seven days a week.' It is not changed.
Der Notdienst ist rund um die Uhr erreichbar.
The emergency service is available around the clock.
about / approximately
'etwa' and 'rund' can both come before numbers and show that a statement is not completely exact. In this use, they are often interchangeable: 'etwa 100 Euro' and 'rund 100 Euro' mean almost the same thing. 'etwa' is very general and also works with time, quantity, or distance. 'rund' is especially common with numbers and often sounds a bit more factual. They can be confused because 'rund' can also describe a shape. With numbers, however, 'rund' does not refer to the shape, but to an approximate figure.

Beim Termin spricht die Chefin über rund fünfzig neue Kunden.
At the meeting, the boss talks about around fifty new customers.
Die Reparatur dauert etwa zwei Stunden.
The repair takes about two hours.