A ocean is a body of water that consists of salt water. A large part of the earth is covered with sea water, more than two-thirds. There are individual parts, but they are all connected. This is called the "world ocean." Usually it is divided into five oceans.
In addition, parts of an ocean also have special names, such as secondary seas and bays. The Mediterranean Sea is an example of this, or the Caribbean Sea. The Red Sea between Egypt and Arabia is more of a tributary sea, almost completely enclosed by land.
The surface of the earth is mainly covered by the oceans: it is about 71 percent, almost three quarters. The deepest point is in the Mariana Trench in the Pacific Ocean. There it is about eleven thousand meters deep.