A sea is a body of water consisting 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". It is usually divided into five oceans.
In addition, parts of an ocean also have special names, such as side seas and bays. The Mediterranean Sea is an example of this, or the Caribbean. 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 seas: it is about 71 per cent, almost three quarters. The deepest point is in the Mariana Trench in the Pacific Ocean. There it is about eleven thousand metres deep.