The term down under
is a colloquialism
referring to things related to, or coming from Australia
(sometimes known as 'the land down under').
"Down Under" is also the title of a song written by the Australian rock group Men at Work which has become a popular patriotic song. This song references vegemite on a sandwich, among other things.
The most well known part of the lyrics is the refrain:
Do you come from a land down under?
Where women glow and men plunder?
Can't you hear, can't you hear the thunder?
You better run, you better take cover.
See also Aussie