If you look at a map of the globe, it's easy to see that there is really only one ocean.
While there is only one global ocean, the ocean is geographically divided into the Atlantic, Pacific, Indian, Arctic, and Southern (Antarctic).
These five oceans are not separate bodies of water; they form one continuous oceanic mass. The boundaries between these five oceans arose over time for a variety of historical, cultural, geographical, and scientific reasons.
The Pacific, the Atlantic and the Indian Oceans are known as the three major oceans.
The Southern Ocean is the 'newest' ocean. The boundaries of this ocean were set in 2000 by the International Hydrographic Organization. The U.S. is a member of this organization, represented by the NOS Office of Coast Survey.