Three quarters of the surface of the Earth is covered by ocean. The ocean is given five names, or there are five "oceans" as follows:
Regions of the oceans are known as seas, gulfs, straits etc. The study of the earth's oceans is called oceanography. The boundaries between the oceans are apparently set by the International Hydrographic Organization, e.g., the Southern Ocean extends from the coast of Antarctica to 60 degrees south latitude.
One of the most dramatic forms of weather occur on the oceans: hurricanes, which are known as typhoons in the Pacific Ocean. Ocean currents greatly affect the earth's weather--for example, El Niño and La Niña in the southern Pacific Ocean greatly affect the weather of The Americas.
The oceans are essential to transportation: a huge portion of the world's goods is moved by ship between the world's main seaports. Important ocean canals include the Saint Lawrence Seaway, Panama Canal, and Suez Canal.