Ytre Oslofjord (Norwegian literally "Outer Oslo Fjord") is that part of Oslofjord which is south of the threshold of Drøbaksund (literally Drøbak Sound), the strait  where the fjord narrows between Drøbak and Hurum, Norway.
Outer Oslo Fjord (Norwegian literally "Outer Oslo Fjord") refers to the portion of Oslofjord situated south of Drøbaksund, a strait where the fjord's width is reduced between Drøbak and Hurum, Norway.