Wiktionary's entry for cookie says a "cookie" is
(England and Wales) A specifically American-style biscuit.
and Wikipedia's entry for biscuit says
Although in Commonwealth Nations, the term "cookie" may be synonymous with "biscuit", a cookie is generally a softer baked product.
I don't really recall "cookie" being used this way 10 or 20 years ago in Australia. Am I imagining it, or has usage of the word increased over time?