Mainland Japan (内地, naichi, lit. "inner lands") is a term to distinguish the area of Japan from its outlying territories. It was an official term in the pre-war period, distinguishing Japan and the colonies in East Asia. After the end of World War II, the term became uncommon, but still is used as an unofficial term to distinguish the area of Japan from Okinawa or Hokkaidō.
The literal Japanese meaning might best be translated as inner Japan or inner lands. The term "mainland" is an inaccurate translation because mainland is usually the continental part of a region, as opposed to the islands.
It is also somewhat confusing as Mainland Japan is defined to consist of several major islands (Hokkaidō, Honshū, Kyūshū, Shikoku) and many minor ones. The term mainland Japan is also sometimes used to translate Honshū, the largest island, though naichi not.
In the Japanese Empire of the pre-war period, naichi referred to the mainland of the empire. The other territories of the empire was called gaichi (外地, lit. "outer lands").
1 of the Common Law (共通法) enumerates the territories with legal jurisdictions, namely,
In other words, Naichi consisted of the following:
Although it has never been abolished, the Common Law lost effect from enforcement after Japan lost all the former colonies, or gaichi as a result of World War II.
The residents of Hokkaidō and Okinawa occasionally use naichi to refer to the "mainland", excluding these areas. The colloquial usage is officially "incorrect", as both areas are legally within naichi. In Hokkaidō, the official term that refers to Japan except Hokkaidō is Dōgai (lit. outside of Hokkaidō). With Dōgai becoming common even in colloquial use, naichi ceases to be used.