WTF is a World Model? [D]

I'm trying to understand what a world model is. I understand it has cognitive science and reinforcement learning. I understand at least at the moment what most people are building which they call world models are fancy video generation models. But what actually counts. Does a simulator count as a world model. Some "world models" are described as simulators, or rather a simulator is described as one type of world model. But is a simulator like lets say a physics engine a world model? There are some video game world models or computer use world models. Would a hardware/video game emulator count as a world model? And can a digital twin also be a world model with some additional features.

I've seen a definition that says a world model should "operate on learned representations, not exclusively hand-crafted physics i.e. a physical referent is optional." Which is fair enough but then would a physics accelerator that uses a ml count as a world model? Like some ML fluid simulator is that a fluid world model?

Are world models just a rebrand of simulation or is there really a fundamental difference? Should the definition be limited to models that aim to generally model all of the real world? So that would exclude video game world models and also models of specific interactions.