wanker - I'm not sure what

this term means but I can probably guess. I think I've heard it used in a rude sense but my understanding is that it is a foreignism and being a hot-blooded-true-blue Australian who is proud of my Australian heritage mostly in the outback, born in Bourke western NSW, Father born in Bourke western NSW, grandparents from around Byrock, Brewarrina, Gongolgon, then I prefer to use Australianisms rather than foreignisms.
So while talking about values, I wonder if the values experts can tell the difference between a billabong and an anabranch; or a coolabah tree from a liquidamber? or a wallaby from a kangaroo; or a sheep from an emu?