is a good place to start.
In what regard are you trying to settle your mind?
"Model" is a fairly broad term, but my interpretation of it is where there is some kind of commercial/monetary aspect involved - usually when the model receives payment for their work, or if a company is profiting from the use of that work, regardless of whether it's fashion shows, catalogues, TV commercials, etc.
I mainly say this because it's not like I can just stand there on the beach and have my photo taken and *WHAM* I'm an instant model.
So unless the person at least has a photographic portfolio and is on a model agency roster then I think it's a bit of a grey area.
I suppose an exception to this would be "art" models, but that's something I have no clue about whatsoever, heh.
This is all my opinion, though.
Maybe someone else can shed a little more light on the matter.