Myth: That in Australian usage flu = influenza.
I disagree with the prevailing cold versus flu opinion in this thread.
I think the majority Australian language and attitude has evolved so that a bad cold is now "the flu", and that influenza must be stated in full and not abbreviated to flu. I don't think any amount of education is going to reach those who say "the flu" for a cold, so it's up to the intelligent minority to adapt.
In a similar vein, "the dreaded lurgy" (one of my mother's favourite ailments) is not related to allergy ('lergy) in any way except etymology.