The Seven Seas is a figurative term that can be traced back to ancient times referring to all the seas and oceans of the world. The correct answer to the question depends on whom you ask, or what reference material you use.
Since the 19th-century experts and encyclopedias will list the Modern Seven Seas as the oceans dividing the Atlantic and Pacific Oceans by the hemispheres:
After the discovery of America during the Age of Discovery (1450-1650), the concept of the Seven Seas was the seven navigable seas of the world at that time:
Before then the Ancient Seven Seas had its origins in Greece and Rome:
And it doesn't end there... The ancient Hindus, Chinese, Persians, Romans and more referred to the Seven Seas as completely different bodies of water.