"A mental model is an explanation of someone's thought process about how something works in the real world. It is a representation of the surrounding world, the relationships between its various parts and a person's intuitive perception about his or her own acts and their consequences" this is from wikipedia https://en.wikipedia.org/wiki/Mental_model - but I remember also similar definitions from other sources.

I would say all thinking is about building a mental model - it is what lets you predict how something will behave in a particular circumstance. Some mental models are not very reusable, some are applicable in many places - and it seems useful to collect the more universal models.