Between two rivers, what was that industrial region? (4)

I believe the answer is:

ruhr

I'm a little stuck... Click here to teach me more about this clue!

'industrial region?' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for ruhr that I've seen before include "German industrial region" , "Major industrial region of north-west Germany" , "River and industrial region of northwest Germany" , "German industrial zone, river" , "Traditional region of German heavy industry" .)

I've seen this clue in The Independent.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.