An ocean (from Ancient Greek Ὠκεανός, transc. Okeanós, the sea of classical antiquity[1]) is a body of saline water that composes much of a planet’s hydrosphere.[2] On Earth, an ocean is one of the major conventional divisions of the World Ocean, which occupies two-thirds of the planet’s surface. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern, and Arctic Oceans.[3][4] The word sea is often used interchangeably with “ocean” in American English but, strictly speaking, a sea is a body of saline water (generally a division of the world ocean) partly or fully enclosed by land.[5]

Saline water covers approximately 72% of the planet’s surface (~3.6×108 km2) and is customarily divided into several principal oceans and smaller seas, with the ocean covering approximately 71% of the Earth’s surface.[6] The ocean contains 97% of the Earth’s water, and oceanographers have stated that only 5% of the World Ocean has been explored.[6] The total volume is approximately 1.3 billion cubic kilometers (310 million cu mi)[7] with an average depth of 3,682 meters (12,080 ft).[8]