Apartments (5)
(Other definitions for units that I've seen before include "Apparatus similar to barbecue" , "Figure on the right" , "Individual things as parts of a whole" , "Detachments" , "Measures of alcohol" .)
'apartments' is the definition.
('flat' can be a synonym of 'apartment')
This is the entire clue.
(Other definitions for flats that I've seen before include "As opposed to sharps?" , "Apartments" , "Punctures" .)