From Longman Dictionary of Contemporary Englishred-light districtˌred-ˈlight ˌdistrict noun [countable] SYSEX/HAVE SEX WITHthe area of a town or city where there are many prostitutes
Examples from the Corpus
red-light district• These streets were the core of the Barbary Coast red-light district.• Sabino Alley still sheltered the vestiges of the old red-light district.• Budapest Week will move over the river to the red-light district in Budapest, where Duna's headquarters are situated.• Anti-vice campaigners like former boxer, Eddie Neilson have all but cleared up the red-light district. 