The way maths is taught in Australia, for a long time the term function was synonymous with the concept "2D plot that passes the vertical line test" in my mind.

The way maths is taught in Australia, for a long time the term function was synonymous with the concept "2D plot that passes the vertical line test" in my mind. I was completely unaware of how much broader and more interesting a concept functions are. There are probably many people whose understanding never progresses beyond this, which I think this is extremely unfortunate.