Since 1949m the KMT officials deliberately and misleadingly translated mainland as 大陸, which actually means the continent in Chinese. That’s why many people would rhetorically ask “which 大陸?” since there are at least 5 or 7 continents, none of which is a country. Mainland should have been translated to 本土 instead.
The reason why I say the KMT did it on purpose is that when “mainland” is used in the American context, like Hawai’i and the US mainland, the translation would always be 美國本土, you would never see the term 美國大陸. You would only see 美洲大陸 in Taiwan,which refers to the Americas as continents.
The Japanese used the kanji 內地 (interior) when during the Japanese era when referring to the Japanese home islands. Right now China is insisting that Taiwanese and Taiwanese celebrities use that term to refer to China as well. Many Taiwanese people would usually rhetorically ask “interior? you mean Nantou county?”