What does a continent have?

The question is "What does a continent have?" in the sense of "What are the characteristics that cause us to call something a continent"? If so, a continent is simply a large enough land mass to miss being called an island. Australia is right on the edge of the decision (it's a continent) and so would Antarctica be if all the snow melted.

If the determination was strictly geological, Europe and Asia would be one continent together, probably called "Eurasia." However, the people who made these determinations were Europeans, and they were impressed by the differences in culture between the two places, so they seperated them, linguistically if not physically.

By an interesting circumstance, long after the division by culture had occurred, scientists discovered that Europe and Asia actually are, or were, separate continents that smashed into each other long, long ago, raising the Ural Mountains, which, sure enough, are considered the border between the two. We actually got it right.