Avilon is the continent, though it is known the world is round and there are other continents. No one has ever been fortunate enough to return from any voyage attempting to reach the other continents. It is claimed that someone in Islandia is building a massive ship the goal of which is to travel the world, with five hulls and crewed by over a thousand.
It is widely believed that the Powers That Be protect Avilon from being engaged with the wider world. Much of what we know comes from Paria, in terms of mapping.