The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth and contains 97% of Earth's water. Another definition is "any of the large bodies of water into which the great ocean is divided".

The 5 oceans are: Pacific (the largest), Atlantic, Indian, Southern (Antarctic), and Arctic (the smallest). Seawater covers approximately 361,000,000 km2 (139,000,000sq mi) of the planet.

It is the principal component of the Earth's hydrosphere, and therefore integral to life on Earth. Acting as a huge heat reservoir, the ocean influences climate and weather patterns, the carbon cycle, and the water cycle.

Ocean temperatures depend on the amount of solar radiation reaching the ocean surface. In the tropics, surface temperatures can rise to over 30 °C (86 °F). Near the poles where sea ice forms, the temperature in equilibrium is about −2 °C (28 °F). Deep seawater temperature is between −2 °C (28 °F) and 5 °C (41 F)

The ocean is subject to numerous environmental threats, including marine pollution, overfishing, The continental shelf and coastal waters that are most influenced by human activity are especially vulnerable.

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