The eastern four-fifths of the giant Eurasian landmass, Asia is more a geographic term than a homogeneous continent. It has the greatest range of land elevation of any continent, has the longest coastline, is subject overall to the world's widest climatic extremes, and, consequently, produces the most varied forms of vegetation and animal life on Earth. In addition, the peoples of Asia have established the broadest pattern of human adaptation found on any of the continents.

The name Asia is ancient, and its origin has been variously explained. The Greeks used it to designate the lands situated to the east of their homeland. It is also believed that the name may be derived from the Assyrian word asu, meaning "east." Another possible explanation is that it was originally a local name given to the plains of Ephesus and gradually extended to include Anatolia (contemporary Asia Minor, which is the western extreme of mainland Asia) and the rest of the continent.

Asia is bounded by the Arctic Ocean on the north, the Pacific Ocean on the east, the Indian Ocean on the south, the inland seas of the Atlantic Ocean--the Mediterranean and the Black--on the southwest, and Europe on the west. Asia is separated from North America to the northeast by the Bering Strait and from Australia to the southeast by the mingled waters of the Indian and Pacific oceans. The Isthmus of Suez unites Asia with Africa, and it is generally agreed that the Suez Canal forms the border between them. Two narrow straits, the Bosporus and the Dardanelles, separate Anatolia from the Balkan Peninsula.

The land boundary between Asia and Europe is a historical and cultural construct that is subject to various interpretations; only as a matter of agreement is it tied to a specific borderline. The most convenient geographic boundary--one that has been adopted by most geographers--is a line that runs south from the Arctic Ocean along the eastern slope of the Ural Mountains and then turns southwest along the Zhem River to the northern shore of the Caspian Sea; west of the Caspian, the boundary follows the Kuma-Manych Depression to the Sea of Azov and the Kerch Strait.

The total area of Asia, including the Caucasian isthmus and excluding the island of New Guinea, amounts to about 17,226,000 square miles (44,614,000 square km). The islands--Severnaya Zemlya, the New Siberian Islands, Wrangel Island, Sakhalin, the Kurils, Japan, the Ryukyus, Taiwan, Hainan, the Philippines, Indonesia and insular Malaysia, the Andaman and Nicobar islands, Sri Lanka, and Cyprus--account for about 1,240,000 square miles (3,210,000 square km) of the total (although New Guinea is mentioned occasionally in this article, it generally is not considered to be a part of Asia). The farthest terminal points of the Asian mainland are Cape Chelyuskin in north-central Siberia, Russia (77º43' N), to the north; the tip of the Malay Peninsula, Cape Piai, or Bulus (1º16' N), to the south; Cape Baba in Turkey (26º4' E) to the west; and Cape Dezhnyov, or East Cape (169º40' W), in northeastern Siberia, overlooking the Bering Strait, to the east.

Asia has the highest average elevation of the continents and contains the sharpest relief. The highest peak in the world, Mount Everest, which is 29,028 feet (8,848 meters) high; the lowest place on the Earth's land surface, the Dead Sea, which averages about 1,312 feet (400 meters) below sea level; and the world's deepest continental trough, occupied by Lake Baikal, which is 5,315 feet (1,620 meters) deep and whose bottom lies at 3,822 feet (1,165 meters) below sea level, are all located in Asia. These physiographic extremes and the overall predominance of mountain belts and plateaus are the result of Asia's prolonged and intense geologic activity. Asia is the youngest of the continents; broadly speaking, it consists of several ancient platform cores, which over time accumulated immense quantities of material around them and were subjected to a series of collisions with one another that resulted in uplifting along the zones of collision.

Asia's coastline--some 39,000 miles (62,800 km) in length--is, variously, high and mountainous, low and alluvial, terraced as a result of the land being uplifted, or "drowned" where the land has subsided. The specific features of the coastline in some areas--especially in the east and southeast--are the result of active volcanism; of thermal abrasion (resulting from a combination of action by sea breakers and of thawing) by the subterranean fossilized ice (consisting of fossil ice, subsurface ice, and ice-formed rock), as in northeastern Siberia; and of coral building, as in the areas to the south and southeast.

The mountain systems of Central Asia not only have provided the continent's great rivers with water from their melting snows but also have formed a forbidding natural barrier that has influenced the movement of peoples into the area. Migration has been possible only through mountain passes. As a result, the historic movement of population has been broadly from the arid zones of Central Asia through the mountain passes into the Indo-Pakistan subcontinent, from China through Southeast Asia to modern Indonesia and Malaysia, and from the Arabian Peninsula and from India across the Bay of Bengal into Indonesia and Malaysia. The Korean and Japanese people and, to a lesser extent, the Chinese have remained ethnologically more homogeneous than the populations of other Asian countries.

Also as a result of this configuration, Asia's population is unevenly distributed. There is a concentration of population in western Asia as well as great concentrations in the Indo-Pakistan subcontinent and the eastern half of China and appreciable concentrations in the Pacific borderlands and on the islands; but vast areas of Central and North Asia have remained sparsely populated. Nonetheless, Asia, the most populous of the continents, contains almost three-fifths of the world's people.

Asia is the birthplace of all the world's major religions--Buddhism, Christianity, Hinduism, Islam, and Judaism--and of many minor ones. Of these, only Christianity developed primarily outside Asia; it exerts little influence on the continent, though many Asian countries have Christian minorities. Buddhism has had a greater impact outside its birthplace in India and is prevalent in various forms in China, Korea, Japan, the Southeast Asian countries, and Sri Lanka. Islam has spread out of Arabia eastward to South and Southeast Asia, as well as westward and southward to Africa. Hinduism has been mostly confined to the Indian subcontinent.