未知的南方大陆（拉丁语：Terra Australis Incognita）是15世纪至18世纪时，欧洲地图上出现的假想大陆。别名墨瓦腊泥加（拉丁语：Magallanica / Magellanica, 斐迪南·麦哲伦的国）。

未知的南方大陆这个想法最初是由亚里士多德提出来的，这个观念后来由托勒密进一步扩展，他并相信印度洋就位在南方大陆的附近，因为这样才能与北半球的大陆达成平衡。

澳大利亚的英文「Australia」源于拉丁文「australis」（南方）。

阿非利加洲
（非洲）

南极洲

亚洲

澳大利亚洲

欧罗巴洲
（欧洲）

Terra Australis (Latin for South Land) was a hypothetical continent first posited in Antiquity and which appeared on maps between the 15th and 18th centuries. Although the landmass was drawn onto maps, Terra Australis was not based on any actual surveying of such a landmass but rather based on the hypothesis that continents in the Northern Hemisphere should be balanced by land in the south. This theory of balancing land has been documented as early as the 5th century on maps by Macrobius, who uses the term Australis on his maps.