What is the difference between an ocean and a sea? What is the difference between an ocean and a sea? An ocean is a vast body of water encompassing 70% of Earth, whereas a sea refers specifically to a large, inland, saline body of water. Seas are generally smaller than an ocean and tend to be partially enclosed by land or large, inland, saline water bodies. The term sea is used to describe the global, interconnected water body covering 70% of Earth's surface, whereas oceans refer to the individual basins within this global sea. There is no difference, just a different term for the same physical feature.