Australia refers to both the continent of Australia and to the Commonwealth of Australia, the sovereign country. Australia, the world's smallest continent & largest island, in the Southern Hemisphere and is bordered by both the Indian Ocean, Pacific Ocean & Southern Ocean.
The term Australia was used in various instances referring to different places in the South Pacific region before naming Australia the country. By the end of the 18th century, the name was being used to refer specifically to Australia, with the botanists George Shaw and Sir James Smith writing of "the vast island, or rather continent, of Australia, Australasia or New Holland" in their 1793 Zoology and Botany of New Holland, and James Wilson including it on a 1799 chart.
As early as 1804, the name Australia was popularised by the explorer Matthew Flinders, who pushed for it to be formally adopted.
There is no probability, that any other detached body of land, of nearly equal extent, will ever be found in a more southern latitude; the name Terra Australis will, therefore, remain descriptive of the geographical importance of this country, and of its situation on the globe: it has antiquity to recommend it; and, having no reference to either of the two claiming nations, appears to be less objectionable than any other which could have been selected. FOOTNOTE: Had I permitted myself any innovation on the original term, it would have been to convert it to AUSTRALIA; as being more agreeable to the ear, and an assimilation to the names of the other great portions of the earth. (Matthew Flinders)
A despatch to Lord Bathurst of 4 April 1817 in which Governor Lachlan Macquarie acknowledges the receipt of Capt. Flinders' charts of Australia appears to be the first time that australis was referred to as Australia. On 12 December 1817, Macquarie recommended to the Colonial Office that it be formally adopted. In 1824, the Admiralty agreed that the continent should be known officially as Australia.
The country has been referred to colloquially as Oz since the early 20th century. Aussie is a colloquial term for "Australian". The noun "Aussie" can also be used to refer to the nation. The sporting anthem C'mon Aussie C'mon is an example of local use of Aussie as synonym for Australia.