In the Korean "Chinese Character Dictionary," it is explained as follows:
The character "洞 (dong)" has "氵" on the left side, which represents "water." Combined with the right part "同 (tong)," it indicates a "place with water," and in ancient times, it came to mean "village." Nowadays, "동 (dong)" in Korean refers to "street" and has no relation to the Chinese meaning of "mountain cave (洞)."
In South Korea, there are over 2,000 dong areas, with Seoul alone having 522. Among these, the most famous is undoubtedly Myeong-dong in Seoul.