der Großraum
metropolitan area
An extended geographic region that includes a metropolis and its surrounding area; an urban agglomeration.
Im Großraum Frankfurt gibt es viele Arbeitsplätze.
There are many jobs in the greater Frankfurt area.

metropolitan area / open-plan space
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metropolitan area
An extended geographic region that includes a metropolis and its surrounding area; an urban agglomeration.
Im Großraum Frankfurt gibt es viele Arbeitsplätze.
There are many jobs in the greater Frankfurt area.

The word is a simple compound of 'groß' (large) and 'Raum' (space/area). So it describes either a large geographic region or a large, open interior space.
Das Unternehmen hat seinen Sitz im Großraum Stuttgart.
The company is based in the greater Stuttgart area.
You can recognize the meaning from the context. If 'Großraum' (metropolitan area) appears with the name of a city, it refers to the geographic region. In connection with 'Büro' (office) or 'Wagen' (coach/car), it refers to an open interior space.
Der öffentliche Nahverkehr im Großraum Hamburg wird ausgebaut.
Public transport in the greater Hamburg area is being expanded.
In the meaning of 'open interior space', 'Großraum-' is very often used as the first part of a new word. The most common examples are 'das Großraumbüro' (open-plan office) and 'der Großraumwagen' (open coach, on a train).
Die Arbeit im Großraumbüro kann sehr laut sein.
Working in an open-plan office can be very noisy.
region
'die Region' and 'der Großraum' both refer to a larger geographical area. However, 'Region' is broader and can mean many kinds of areas, for example a wine region, a coastal region, or a mountain region. 'Großraum' is usually used for a large city and the area around it. 'Großraum' is especially natural when talking about transportation, housing, or work. Learners may confuse the words because a 'Großraum' is also a kind of region. If you mean a metropolis with its surrounding area, 'Großraum' is more precise; otherwise, 'Region' is often more suitable.

Wegen des starken Verkehrs braucht man im Großraum München oft viel Geduld.
Because of the heavy traffic, you often need a lot of patience in the greater Munich area.
Meine Kollegin kennt die Region gut, weil sie dort aufgewachsen ist.
My colleague knows the region well because she grew up there.