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Terminology

The continent of Australia is sometimes known by the names Sahul, Australinea, or Meganesia to differentiate it from the country of Australia, and consists of the landmasses which sit on Australia's continental plate. This includes mainland Australia, Tasmania, and the island of New Guinea, which comprises Papua New Guinea and Western New Guinea (Papua and West Papua, provinces of Indonesia). The name "Sahul" takes its name from the Sahul Shelf, which is part of the continental shelf of the Australian continent.

The term Oceania, originally a "great division" of the world in the 1810s, was replaced in English language countries by the concept of Australia as one of the world's continents in the 1950s. Prior to the 1950s, before the popularization of the theory of plate tectonics, Antarctica, Australia and Greenland were sometimes described as island continents, but none were usually taught as one of the world's continents in English-speaking countries. Scottish cartographer John Bartholomew wrote in 1873 that, "the New World consists of North America, and the peninsula of South America attached to it. These divisions generally themselves spoken as continents, and to them has been added another, embracing the large island of Australia and numerous others in the Ocean, under the name of Oceania. There are thus six great divisions of the earth — Europe, Asia, Africa, North America, South America and Oceania."

The American author Samuel Griswold Goodrich wrote in his 1854 book History of All Nations that, "geographers have agreed to consider the island world of the Pacific Ocean as a third continent, under the name Oceania." In this book the other two continents were categorized as being the New World (consisting of North America and South America) and the Old World (consisting of Africa, Asia and Europe). In his 1879 book Australasia, British naturalist Alfred Russel Wallace commented that, "Oceania is the word often used by continental geographers to describe the great world of islands we are now entering upon" and that "Australia forms its central and most important feature." He did not explicitly label Oceania a continent in the book, but did note that it was one of the six major divisions of the world. He considered it to encompass the insular Pacific area between Asia and the Americas, and claimed it extended up to the Aleutian Islands, which are among the northernmost islands in the Pacific Ocean. However, definitions of Oceania varied during the 19th century. In the 19th century, many geographers divided up Oceania into mostly racially-based subdivisions; Australasia, Malaysia (encompassing Malay Archipelago), Melanesia, Micronesia and Polynesia.

Today, the Malay Archipelago is typically considered part of Southeast Asia, and the term Oceania is often used to denote the region encompassing the Australian continent, Zealandia, and various islands in the Pacific Ocean that are not included in the seven-continent model. It has been recognized by the United Nations as one of the world's five major continental divisions since its foundation in 1947, along with Africa, Asia, Europe and the Americas. The UN's definition of Oceania utilizes four of the five subregions from the 19th century; Australasia, Melanesia, Micronesia, and Polynesia. They include American Samoa, Australia and their external territories, the Cook Islands, Easter Island (Chile), the Federated States of Micronesia, French Polynesia, Fiji, Galapagos Islands (Ecuador), Guam, Kiribati, the Marshall Islands, Nauru, New Caledonia, New Zealand, Niue, the Northern Mariana Islands, Ogasawara (Japan), Palau, Papua New Guinea, Pitcairn Islands, Samoa, the Solomon Islands, Tokelau, Tonga, Tuvalu, Vanuatu, Wallis and Futuna, Western New Guinea, and the United States Minor Outlying Islands (Baker Island, Howland Island, Jarvis Island, Midway Atoll, Palmyra Atoll, and Wake Island) as well as Hawaii, one of 50 states of United States. The original UN definition of Oceania from 1947 included these same countries and semi-independent territories, which were mostly still colonies at that point.

The island states of Indonesia, Japan, the Philippines, Singapore and Taiwan, all located within the bounds of the Pacific or associated marginal seas, are excluded from the UN definition. The states of Hong Kong and Malaysia, located in both mainland Asia and marginal seas of the Pacific, are also excluded, as is the nation of Brunei, which shares the island of Borneo with Indonesia and Malaysia. Further excluded are East Timor and Indonesian (or Western) New Guinea, areas which are biogeographically or geologically associated with the Australian landmass. This definition of Oceania is used in statistical reports, by the International Olympic Committee, and by many atlases. The CIA World Factbook also categorize Oceania or the Pacific area as one of the world's major continental divisions, but use the term "Australia and Oceania" to refer to the area. Their definition does not include Australia's subantarctic external territory Heard Island and McDonald Islands, but is otherwise the same as the UN definition, and it is also used for statistical purposes.

In countries such as Argentina, Brazil, China, Chile, Costa Rica, Ecuador, France, Greece, Italy, Mexico, the Netherlands, Peru, Spain, Switzerland or Venezuela, Oceania is treated as a continent in the sense that it is "one of the parts of the world", and Australia is only seen as an island nation. In other countries, including Kazakhstan, Poland and Russia, Australia and Eurasia are thought of as continents, while Asia, Europe and Oceania are regarded as "parts of the world". In the Pacific Ocean Handbook (1945), author Eliot Grinnell Mears wrote that he categorized Australia, New Zealand and Pacific islands under the label of Oceania for "scientific reasons; Australia's fauna is largely continental in character, New Zealand's are clearly insular; and neither Commonwealth realm has close ties with Asia." He further added that, "the term Australasia is not relished by New Zealanders and this name is too often confused with Australia." Some 19th century definitions of Oceania grouped Australia, New Zealand and the islands of Melanesia together under the label of Australasia, in other 19th century definitions of Oceania, the term was only used to refer to Australia itself, with New Zealand being categorized with the islands of Polynesia in such definitions.

Archaeological terminology for this region has changed repeatedly. Before the 1970s, the single Pleistocene landmass was called Australasia, derived from the Latin australis, meaning "southern", although this word is most often used for a wider region that includes lands like New Zealand that are not on the same continental shelf. In the early 1970s, the term Greater Australia was introduced for the Pleistocene continent. Then at a 1975 conference and consequent publication, the name Sahul was extended from its previous use for just the Sahul Shelf to cover the continent.

In 1984 W. Filewood suggested the name Meganesia, meaning "great island" or "great island-group", for both the Pleistocene continent and the present-day lands, and this name has been widely accepted by biologists. Others have used Meganesia with different meanings: travel writer Paul Theroux included New Zealand in his definition and others have used it for Australia, New Zealand and Hawaii. Another biologist, Richard Dawkins, coined the name Australinea in 2004. Australia–New Guinea has also been used.