This essay breaks down the term “world model” by tracing it to the POMDP perception-action loop and identifying its key components—renderers, simulators, planners, and their connecting loop. It shows how different AI fields project parts of this loop to build spatial and temporal understanding beyond language models.

• The term "world model" is overloaded—video generators with impossible physics and precise physics engines both claim the label, which confuses the field.
• Decomposing the POMDP loop into renderer (state→observation), simulator (action→state), and planner (observation→action) explains why different fields define "world models" so differently.
• Computer vision, robotics, and generative AI each project only one slice of this same underlying loop, rather than building genuinely different concepts.