1.
the (Japanese) mainland; the main islands
In modern Japanese, mostly used by people from Hokkaido or Okinawa to refer to the main island of Honshu (and sometimes Honshu plus Shikoku and Kyushu). Roughly "the rest of Japan" from the speaker's perspective.
2.
the interior of a country; inland area
An inland part of a country, away from the coast or frontier. Less common; appears in some formal or older texts.
Compound of 内 (inner) + 地 (land). In pre-war usage, also meant "Japan proper" as opposed to colonial territories — that usage is now historical and avoided.
Common collocations
- 内地から来る: to come from the mainland
- 内地に帰る: to return to the mainland
- 内地勤務: assignment on the mainland
- 内地留学: study at a mainland school (Hokkaido/Okinawa usage)
Usage
The "mainland" sense is most natural from a Hokkaido or Okinawa perspective. Honshu speakers rarely call their own islands 内地; for them it just sounds like the speaker is from somewhere else.