Many people use the terms "ocean" and "sea" interchangeably when speaking about the ocean, but there is a difference between the two terms when speaking of geography (the study of the Earth's surface).

An ocean is a large expanse of salt water that covers three-quarters of the earth's surface. It is bounded by the continents, or the equator, and other imaginary lines. The Earth's seven main oceans are; the Arctic, North Atlantic, South Atlantic, North Pacific, South Pacific, Indian and Antarctic Oceans. These main oceans comprise the "world ocean". A sea on the other hand, is a body of salt water that is surrounded by land on all or most sides, or that is part of one of the oceans. For example, the Caspian Sea and the Dead Sea are large saline lakes that are surrounded by land - they lack a natural outlet; the Sargasso Sea is a portion of the Atlantic Ocean and the Mediterranean Sea is attached to the Atlantic Ocean.

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