Oceania also known as Oceanica, is a region centred on the islands of the tropical Pacific Ocean. Opinions of what constitutes Oceania range from its three subregions of Melanesia, Micronesia, and Polynesia to, more broadly, the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago.

The term is often used more specifically to denote a continent comprising Australia and proximate islands or biogeographically as a synonym for either the Australasian ecozone (Wallacea and Australasia) or the Pacific ecozone (Melanesia, Polynesia, and Micronesia apart either from New Zealand[11] or from mainland New Guinea).

As an ecozone, Oceania includes all of Micronesia, Fiji, and all of Polynesia except New Zealand. New Zealand, along with New Guinea and nearby islands, part of Philippines islands, Australia, the Solomon Islands, Vanuatu, and New Caledonia, constitute the separate Australasian ecozone. In geopolitical terms, however, New Zealand, the Solomon Islands, Vanuatu and New Caledonia are almost always considered part of Oceania, and Australia and Papua New Guinea are usually considered part of Oceania too. Sometimes Papua province in Indonesia may be included, as Puncak Jaya is often considered the highest peak in Oceania

Countries of Australia and Oceania
The “continent” of Australia/Oceania is a somewhat artificial construct, designed to link together the continental landmass of Australia with the huge number of widely scattered islands across the Pacific Ocean.

Area: 8 600,000 km2 (3 300,000 mi2)
Population: 37 million
Highest Point: Puncak Jaya (Carstensz Pyramid 4884 m/16 023 ft), Papua Province, Indonesia
Largest Lake: Lake Eyre, Australia (if there is some water)
Longest River: Murray-Darling river system 3750 km (2300 mi)

Languages of Oceania: Melanesian pidgin, Melanesian-Polynesian Languages, English, French.

From Wikipedia