South Korea and Japan have different opinions about internationally used names in the sea between the two countries. The two countries is completely different name and to use only one of these it is not correct and especially only use the name "Sea of Japan" is just Japan's wrong claim.

The International Hydrographic Organization Technical Resolution and the United Nations Resolution on the Standardization of Geographical Names recommend that countries sharing a geographical area, but use different names to refer to the area, should endeavor to reach an agreement on a single name. 

Should they fail to reach an agreement, the name used by each country involved should be concurrently adopted for charts and publications.

Japan insists that the United Nations (UN) has officially approved of the name Sea of Japan, which is not exactly true. It is not the UN that uses the name Sea of Japan, but only its secretariat, a principal arm of the UN. Therefore, the secretariat using only the Sea of Japan does not represent the opinion of all 192 members of the UN.

Furthermore, the UN Secretariat uses only the Sea of Japan according to its internal practice which spells out that "for any names in dispute, it uses the most widely used name before relevant parties reach the agreement."