What does 地道 (지도) mean in China?

ANSWER: As a noun, 地道 (지도) can mean either "tunnel" or "causeway," but as an adjective, it means either "authentic," "genuine," or "proper."

By itself, the character 地 (지) can mean "ground," "earth," "land" or "place." And by itself, 道 (도) can mean either "road" or "path." So, together 地道 (지도) literally means "ground (地) road (道)," where "ground" here seems to mean "underground (地下 지하)."

So, in China, I guess the phrase 地道地道 (지도지도) could be translated as "a (一個) real (地道) tunnel (地道)," not a fake one.

By the way, in Taiwan, 地道 (지도) is also used to mean "tunnel," but it is not used to mean "authentic." Instead, in Taiwan, they switch the characters and write 道地 (도지) to mean "authentic."