We inhabit Worlds – both physical and conceptual. We learn how to work and behave within them. We engage in tribalism, spatial reasoning, and territorialism, even within Worlds that live entirely in our minds. We have a sense for the boundaries of Worlds and their ruletsets.

Worlds exist within books, games, social groups, and religions. Amongst those, we can find The World of Narnia, Christianity, and the Commonwealth Law.

Worlds run on everything from letters to wikis, bedtime stories, constitutions, databases, and, most importantly, our collective human intelligence. To say that a World "runs" on X is to say that X is the reason for the persistence of the World, the reason why we continue experiencing the container as a World, as being alive.

Worlds sometimes live entirely within the minds of people, with some light physical footprints: books, computer memory, etc. However, the physical artifacts of such Worlds are not the reason that these Worlds are alive. Printing a million copies of a book doesn’t create a World, unless people read it, care about it, and inhabit it.