The terms “the ocean” or “the sea” used without specification refer to the interconnected body of salt water covering the majority of the Earth’s surface. It includes the Atlantic, Pacific, Indian, Southern and Arctic Oceans. As a general term, “the ocean” and “the sea” are often interchangeable, although speakers of British English refer to “the sea” in all cases, even when the body of water is one of the oceans.
Strictly speaking, a “sea” is a body of water (generally a division of the world ocean) partly or fully enclosed by land. The word “sea” can also be used for many specific, much smaller bodies of seawater, such as the North Sea or the Red Sea. There is no sharp distinction between seas and oceans, though generally seas are smaller, and are often partly (as marginal seas) or wholly (as inland seas) bordered by land.