Line divides whole ghetto (4)
I believe the answer is:
slum
'ghetto' is the definition.
(I've seen this in another clue)
'line divides whole' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'divides' is an insertion indicator (inserted letters create a division or opening).
'whole' becomes 'sum' (sum is a kind of whole).
'l' put into 'sum' is 'SLUM'.
(Other definitions for slum that I've seen before include "Poor-quality accommodation" , "Area of poor housing" , "Over-crowded run-down city area" , "Area of bad housing" , "Squalid, overcrowded dwelling" .)