A previous misconception of the ocean is that there were  five oceans, however in reality we have 1 ocean with many basins. the most prominent of which consists of the North Pacific, South Pacific, North Atlantic, South Atlantic, Indian, Southern, and Arctic. These seven basins are where the concept of the seven seas came from. 

In reality, seas are considered distinct from the one global ocean. Although all seas are interconnected by the ocean, they are typically smaller basins that are partially enclosed by land 

Oceanic basins consist of various features and depths, with the deepest part of the ocean being the Marianas trench, which drops to a depth of 11000m. Earth’s highest peaks, deepest valleys, and flattest plains are all in the ocean. Mauna Kea in Hawaii is considered the tallest mountain in the world when measured from its base on the ocean floor.

Much like terrestrial environments the geology of the ocean floor is extremely diverse. Some formations include continental shelves, mid-ocean ridges, deep sea trenches, Underwater volcanoes as well as  many more.  learn more about ocean features here 

The deepest part of the ocean is Known as Challenger Deep. Challenger Deep sits at the very bottom of the Marianas trench at a depth of 10935m or 35876 feet.  The Marianas Trench runs several hundreds of kilometres southwest of Guam. only three people have ever visited the bottom of Challenger Deep, one of them being James Cameron

The deepest point in the southern hemisphere is located in the depths of the Tonga Trench at a depth of 10800m closely followed by the Kermadec Trench Which is 150km north of New Zealand