The term prefecture (from the Latin Praefectura) indicates the office, seat, territorial circonscription of a Prefect; consequentally, like that word, is its applied in English in relation to actual Prefects, whose title is just that (or the forms it takes in other, especially Romance, languages), in the broadest sense in the Roman tradition, but also by analogy, more or less conventionally, to render offices deemed equivalent in other languages' cultural traditions.
Greek equivalent of prefecture
Modern Greece, under its 1975 Constitution, is divided into 51 nomoi (Greek: νομοί) which form the units of local government. These are most commonly translated into English as prefectures. Each nomos is headed by a prefect (nomarch), who was until recently a ministerial appointee but is nowadays elected by direct popular vote. Municipal elections in Greece are held every four years and voting for the election of nomarchs and mayors is carried out concurrently but with separate ballots.
Prefectures of Greece
Central Greece (Roumeli)