In absence of a better answer, I would say that a system has a world-model if it can answer various questions about the world mostly coherently (i.e. the answers to two different questions should not make completely different assumptions about something).
I have seen the concept of world-model used to talk loosely about a neural networks or an agents understanding of the world, but I was wondering what resources (blog posts, journal articles, etc.) exist that talk more precisely about what is a world-model, what are its parts, how do you know if a given system has one or not, if a system does have one, how do you know its structure, does a system necessarily even have a world-model to begin with, even if it's a trivial one? etc.?