An informal expression for all of the oceans of the world WordNet 3.0 & Open English WordNet

"The Seven Seas" is a figurative term for all the seas of the known world. Wikipedia

All of the oceans of the world. (In a common modern interpretation, the seven seas are the North and South Atlantic, North and South Pacific, Indian, Arctic and Antarctic, but historical interpretations differ widely; see the Wikipedia article for this.). Wiktionary

All of the Earths oceans. Wiktionary (translation)