40 degrees north latitude and 140 degrees east longitude is a point in the northwestern Pacific Ocean, roughly east of the Korean peninsula and south of the Russian island of Sakhalin. It's located in the Sea of Japan, also known as the East Sea.

Keep in mind that coordinates specify a *point* on Earth, not a specific location. It's possible that there are islands, ships, or other objects located at that exact point, but it's not a well-known or named geographical feature.