"Bimyou" has several meanings. It means small, sensitive, fine, subtlety, etc.
In case of sensitive, there is a sensitive issue between man and wife. (夫婦間に微妙な問題がある。)
In case of small, the difference in Korean and Japanese are small from the point of view of European. (ヨーロッパ人から見ると、韓国人と日本人の違いは微妙です。)