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 seven main oceans comprise the “world ocean”. 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; Sargasso Sea is a portion of the Atlantic Ocean and the Mediterranean Sea is attached to the Atlantic Ocean. Major seas include the Mediterranean, Baltic, Bering, Black, Caribbean, Coral, North, Red, and Yellow. The largest seas are the South China Sea, the Caribbean Sea, and the Mediterranean Sea.
Thus, an ocean is interconnected mass of saltwater (covering 71% of the surface of the earth) where boundaries are established by continental land masses, or the equator and ridges in the ocean floor. A sea, on the other hand, is usually smaller than an ocean (a division of an ocean) and is a body of salt water that is; surrounded on all or most sides (partially enclosed) by land and/or part of one of the oceans.