Oceans, seas and sea channels are all saline bodies of water distinguished by their relative sizes, with oceans being the largest, followed by seas and sea channels. Seas and sea channels also are defined by their relationship to land. Oceans, on the other hand, are so large that their relationship to surrounding land is insignificant.
The five oceans on Earth are the Pacific, Atlantic, Indian, Southern and Arctic Oceans. Combined, these large bodies of water cover approximately 72 percent of Earth's surface and comprise more than 97 percent of the water on Earth. Although people often use the words "ocean" and "sea" interchangeably, substituting "sea" for "ocean," they are not the same thing. Seas are also large bodies of saline water, but they are much smaller than oceans and are typically partially surrounded by land. The largest seas on Earth are the Mediterranean Sea in southern Europe, the Caribbean Sea between North and South America, the South China Sea southeast of Asia and the Bering Sea between northern Asia and northern North America. A few bodies of water are labeled as seas even though they don't meet all the criteria; for instance, the Sargasso Sea is an oceanographically distinct body of water even though it is fully surrounded by the Atlantic Ocean, and the so-called Sea of Galilee is actually a freshwater lake. Sea channels are straits that connect two large bodies of water. Notable sea channels include the English Channel and the Strait of Gibraltar.