What term describes the entire body of salt water covering approximately 71% of the earth?

The answer is - Ocean.

All of the oceans in the world are connected, so they practically represent one huge body of water, which is by far the biggest in the planet, and is also a body of water that consist salt, thus it has salty water.

The oceans have sub-divisions, smaller than them, called seas. They range a lot in size, while some are huge, others are smaller than some big lakes. They represent a remote, peripheral part of the oceans, naturally surrounded by some geographical land forms, still they are part of the oceans.