The term Seven Seas has been used throughout history and over time the meaning of this word has changed. Generally speaking, when the is used it refers to a specific set of seas or to the huge amount of water that is out there to sail on.
The term the Seven Seas will mean different things to different people and you will most often see in literature. In medieval European literature the Seven Seas is was referring to Adriatic Sea, the Aegean Sea, the Arabian Sea, the Black Sea, the Caspian Sea, the Indian Ocean, the Irish ea, the Mediterranean Sea, the North Sea, the Persian Gulf, and the Red Sea. When you hear the term the Seven Seas many people have to stop and question which of the seas this includes as the International Hydrographic Organization qualifies 100 different bodies of water as seas.
Many claim that the term the Seven Seas is something that is newer and has origins in Greece and Rome. The term has been found in literature since 2300 BC. In fact, they are referred to around this time in Hymn 8 of the Sumerian Enheduanna to the goddess Inanna.
The term the Seven Seas was also found in a ninth century AD Muslim piece of writing in which the seas are clearly defined. In this writing they referred to the Persian Gulf, the Gulf of Khambhat, the Bay of Bengal, the Strait of Malacca, the Singapore Strait, the Gulf of Thailand, and the South China Sea. This Arabian version of the Seven Seas is obviously different than was thought in Rome and Greece.
In Venice the term the Seven Seas usually just meant that one had sailed through the area lagoons and in Rome this usually meant that one had sailed on seven different bodies of water, and therefore possessed better than average sailing skills. As you can see, the term means different things in different places, and the has been redefined over time. The term today usually is found in stories in books, that are passed down from generation to generation.
Today the Seven Seas are defined differently than they once were, the North Pacific Ocean, the South Pacific Ocean, the North Atlantic Ocean, the South Atlantic Ocean, the Southern Ocean, and the Arctic Ocean, which are not actually seas, but portions of different seas. As you can see, the Seven Seas are different than when the term was first used in the past, and the definition of may very well change in the future.