The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately twenty percent of the Earth's surface and about twenty-six percent of its water surface area. The first part of its name refers to Atlas of Greek mythology, making the Atlantic the "Sea of Atlas".
The oldest known mention of "Atlantic" is in The Histories of Herodotus around 450 BC (Hdt. 1.202.4): Atlantis thalassa (Greek: Ἀτλαντὶς θάλασσα; English: Sea of Atlas); see also: Atlas Mountains. Another name historically used[who?] was the ancient term Ethiopic Ocean, derived from Ethiopia, whose name was sometimes used as a synonym for all of Africa and thus for the ocean. Before Europeans discovered other oceans, the term "ocean" itself was synonymous with the waters beyond the Strait of Gibraltar that we now know as the Atlantic. The Greeks believed this ocean to be a gigantic river encircling the world.
The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between the Americas to the west, and Eurasia and Africa to the east. As one component of the interconnected global ocean, it is connected in the north to the Arctic Ocean (which is sometimes considered a sea of the Atlantic), to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, and the Southern Ocean in the south. (Other definitions describe the Atlantic as extending southward to Antarctica.) The equator subdivides it into the North Atlantic Ocean and South Atlantic Ocean.
The Atlantic Ocean is bounded on the west by North and South America. It connects to the Arctic Ocean through the Denmark Strait, Greenland Sea, Norwegian Sea and Barents Sea. To the east, the boundaries of the ocean proper are Europe; the Strait of Gibraltar (where it connects with the Mediterranean Sea – one of its marginal seas – and, in turn, the Black Sea) and Africa.
In the southeast, the Atlantic merges into the Indian Ocean. The 20° East meridian, running south from Cape Agulhas to Antarctica defines its border. Some authorities show it extending south to Antarctica, while others show it bounded at the 60° parallel by the Southern Ocean.
In the southwest, the Drake Passage connects it to the Pacific Ocean. The man-made Panama Canal links the Atlantic and Pacific. Besides those mentioned, other large bodies of water adjacent to the Atlantic are the Caribbean Sea; the Gulf of Mexico; Hudson Bay; the Arctic Ocean; the Mediterranean Sea; the North Sea; the Baltic Sea and the Celtic Sea.
Covering approximately 22% of Earth's surface, the Atlantic is second in size to the Pacific. With its adjacent seas, it occupies an area of about ; without them, it has an area of . The land that drains into the Atlantic covers four times that of either the Pacific or Indian oceans. The volume of the Atlantic with its adjacent seas is 354,700,000 cubic kilometers (85,100,000 cu mi) and without them 323,600,000 cubic kilometres (77,640,000 cu mi).
The average depth of the Atlantic, with its adjacent seas, is ; without them it is . The greatest depth, , is in the Puerto Rico Trench. The Atlantic's width varies from between Brazil and Sierra Leone to over in the south.
Transatlantic travel played a major role in the expansion of Western civilization into the Americas. It is the Atlantic that separates "Old world" from "New world". In modern times, some idioms refer to the ocean in a humorously diminutive way as the Pond, describing both the geographical and cultural divide between North America and Europe, in particular between the English-speaking nations of both continents. Many British people refer to the USA and Canada as "across the pond", and vice versa.