The term prefecture has been used to denote a self-governing body or area since the time of Constantine I, who divided the Roman Empire into 4 districts (each divided into dioceses). Much like a state or city, these were largely self-governed; however each owed allegiance to Rome. A prefect was the head of a prefecture.
Chinese sense of prefecture
The ancient sense
When used in the context of Chinese history, especially China before the Tang Dynasty, the word "prefecture" is used to translate xian (县/縣). This unit of administration is translated as "county" when used in a contemporary context.
See County of China for more information on the xian of China.
In the context of Chinese history during or after the Tang Dynasty, the word "prefecture" is used to translate zhou (州), another ancient unit of administration in China.
See Zhou (political division) for more information on the zhou of China.
The modern sense
In modern-day People's Republic of China, the prefecture (地区; pinyin: dìqū) is an administrative division found in the second level of the administrative hierarchy. In addition to prefectures, this level also includes autonomous prefectures, leagues, and prefecture-level cities. The prefecture level comes under the province level, and in turn oversees the county level.
See Prefecture of China for more information on modern prefectures in China.
French sense of prefecture
Main article: préfecture
In France, a préfecture is the capital city of a département. By extension, it is also the name of one of the governing bodies of the département. There are 100 préfectures in France.
Greek sense of prefecture
Modern Greece, under its 1975 Constitution, is divided into 51 nomoi (Greek: νομοι). These are most commonly translated into English as prefectures. Each nomos is headed by a prefect (nomarch), who is elected by direct popular vote.
See: Prefectures of Greece
Japanese sense of prefecture
In the Japanese system, the word prefecture is used for translating references to an administrative district, ken (県), which is about the area of a county in the United States but, on average, about half the population of a state.
The local self-governing system of Japan consists of 2 classes: prefectures as the large area local governing units and municipalities the basic local governing units. In the Eastern sense, the administrative segregation of a unified nation is usually trifold: the nation, large area local governing units, and basic local governing units. Japan fits this pattern.
Japan is divided into 47 prefectures and each prefecture is further divided into municipalities. These prefectures and municipalities have no overlapping districts or uncovered areas. In short, all the residents in Japan are sure to belong to one prefecture and one municipality.
These prefectures and municipalities are not merely set up as the nation's administrative section, but also as corporate bodies independent from the country that possesses their own basic governing areas and local residents as their constituents. They hold administrative power within the districts in question. In Okinawa, Nagasaki and Hokkaido, subprefectures are used as special administrative units because such regions are too large or remote for a single prefectural government to govern.
The current prefectural system in Japan was settled in the Meiji era after the new government abolished feudal clans or Han. This is called the "Abolition of the Han system". See Meiji era in History of Japan for historical background of this event.