Fetching details from the dictionary...
within the borders of a country; domestic soil
inland; interior
Japan proper (as opposed to its overseas colonies); homeland; home
"mainland" Japan (i.e. Honshū)
内地で就職するために島を離れた。
I left the island to find work on the mainland.
沖縄では本州のことを内地と呼ぶことがある。
In Okinawa, Honshu is sometimes called naichi.
島民にとって内地は遠い別世界のように感じられる。
For islanders, the mainland feels like a distant, separate world.