Definition and clear working example of Model

Hi,
I have read the Model and Model Configuration part of docs 3 times over and can’t come up with a working mental model of what a model is , and where it is sitting, In the docs it says it is a workspace, (Of what? machines? Application? resources? services? charms?) and provide isolation ( of what?) abstract infrastructre(on Which level?) And ther isn’t an example of a model and what it does and why is it useful.
I could come up with some ideas on what it is just by reading the documents on configuring a model.