der Betrieb
business / company
A business, company, or production facility where people work.
Der Betrieb hat über 500 Mitarbeiter und exportiert in die ganze Welt.
The company has over 500 employees and exports all over the world.

business / operation
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business / company
A business, company, or production facility where people work.
Der Betrieb hat über 500 Mitarbeiter und exportiert in die ganze Welt.
The company has over 500 employees and exports all over the world.

The noun 'der Betrieb' (business / operation) is closely related to the verb 'betreiben' (to operate / to run), which means 'to keep something running' or 'to manage'. This idea of active operation appears in all meanings, from running a company to a machine operating.
Er betreibt ein kleines Café in der Innenstadt.
He runs a small café in the city center.
Fixed expressions are used to describe the start or end of a facility's operation. You say 'etwas in Betrieb nehmen' (to put something into operation) or 'den Betrieb einstellen' (to cease operations).
Die neue Maschine wird morgen in Betrieb genommen.
The new machine will be put into operation tomorrow.
In the meaning 'viel los' (a lot going on) or 'Trubel' (hustle and bustle), 'Betrieb' (activity / bustle) is colloquial. It is used to describe a lively, sometimes chaotic atmosphere.
Am ersten Tag des Schlussverkaufs war in der Stadt ein riesiger Betrieb.
On the first day of the sale, there was a huge amount of activity in the city.
The expression 'außer Betrieb' (out of order) is always used with the verb 'sein' (to be). It describes that a machine or service is temporarily not working.
Die Rolltreppe zum Bahnsteig ist schon wieder außer Betrieb.
The escalator to the platform is out of order again.
company / undertaking
'das Unternehmen' and 'der Betrieb' can both mean an economic unit where people work. 'Unternehmen' tends to emphasize the organization as a whole, for example its goals, management, or economic role. 'Betrieb' often sounds more concrete: you think more of the workplace, production, or day-to-day operations. Learners may confuse the words because both can refer to a company. Be careful: 'Betrieb' can also mean that a machine or system is running, for example 'in Betrieb' (in operation). In that case, it has nothing to do with a company as a business.

In diesem Betrieb arbeiten viele Menschen in der Produktion.
Many people work in production at this company.
Das Unternehmen verkauft seine Produkte inzwischen in mehreren Ländern.
The company now sells its products in several countries.