Nature Ocean

An ocean  is a body of saline water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean, which occupies two-thirds of planet's surface. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern, and Arctic Oceans. The word sea is often used interchangeably with "ocean" in American English but, strictly speaking, a sea is a body of saline water  partly or fully enclosed by land.  Source