The representation that a person has in their mind about the thing they are interacting with. Based on your experience, you’ll create all sorts of abstract (blurry) ideas about how things work. When you flip a switch UP the light goes on, right? It’s muscle memory… but – it doesn’t really match up with how completing a circuit (what is really happening) works. Sometimes our mental models match up to our conceptual models – and they are smart and useful – and other times / it’s just kinda lazy – and it’s just what is left over from our brains autopilot.