Australasia is a region which comprises Australia, New Zealand, and some neighbouring islands. The term is used in a number of different contexts including geopolitically, physiogeographically, and ecologically where the term covers several slightly different but related regions.
Charles de Brosses coined the term (as French Australasie) in Histoire des navigations aux terres australes  (1756). He derived it from the Latin for "south of Asia" and differentiated the area from Polynesia (to the east) and the southeast Pacific ( Magellanica). 
In the late 19th century, the term Australasia was used in reference to the "Australasian colonies". In this sense it related specifically to the British colonies south of Asia: New South Wales, Queensland, South Australia, Tasmania, Western Australia, Victoria (i.e. the Australian colonies) and New Zealand. 
The New Zealand Oxford Dictionary gives two meanings of "Australasia". One, especially in Australian use, is "Australia, New Zealand, New Guinea, and the neighbouring islands of the Pacific". The other, especially in New Zealand use, is just Australia and New Zealand. 
Two Merriam-Webster dictionaries online (Collegiate and Unabridged) define Australasia as "Australia, New Zealand, and Melanesia". The American Heritage Dictionary online recognizes two senses in use: one more precise, being similar to the aforementioned senses, and the other broader, loosely covering all of Oceania.
- de Brosses, Charles (1756). Histoire des navigations aux terres Australes. Contenant ce que l'on sçait des moeurs & des productions des contrées découvertes jusqu'à ce jour; & où il est traité de l'utilité d'y faire de plus amples découvertes, & des moyens d'y former un établissement [History of voyages to the Southern Lands. Containing what is known concerning the customs and products...] (in French). Paris: Durand. Retrieved 2013-12-08.
- Douglas, Bronwen (2014). Science, Voyages, and Encounters in Oceania, 1511-1850. Palgrave Macmillan. p. 6.
- Lee, Joseph (1889). "Anti-Chinese Legislation in Australasia". The Quarterly Journal of Economics. 3 (2). p. 220. JSTOR 1879468.
- Deverson, Tony; Kennedy, Graeme, eds. (2005). "Australasia". New Zealand Oxford Dictionary. Oxford University Press. doi: 10.1093/acref/9780195584516.001.0001. ISBN 9780195584516.
- Richards, Kel (2006). "Australasia". Wordwatch. ABC News Radio. Archived from the original on 2007-03-18. Retrieved 2006-09-30.
- Media related to Australasia at Wikimedia Commons