Run-down area (4)
I believe the answer is:
slum
'run-down area' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for slum that I've seen before include "Run-down housing area" , "Area of poor housing" , "Area of bad housing" , "Poor-quality accommodation" , "Run-down area of city with tenements" .)