A mannerism or slang originating in, or widely used within Australia.
Due to the Crocodile Dundee movies, many people mistakenly believe, "Throw another shrimp on the barbie" to be an Australianism. In fact, in Australia, shrimp are known as prawns; and snags or steak are more likely to be associated with barbeques.
An Australian slant on a word or words.
Billy lid means kid, trouble and strife means wife are well known Australianism's