What is a model?

I built a lot of plastic models in my life such as airplanes, tanks, figures, and ships, but I am not talking about that type of models. So, what am I talking about? What is a model? If a person poses for photographers not for the purposes of displaying and advertising for a product but for her own physique, is she a model?

Here is part of the definition of a model from Dictionary.com:

4. a person or thing that serves as a subject for an artist, sculptor, writer, etc.
5. a person whose profession is posing for artists or photographers.
6. a person employed to wear clothing or pose with a product for purposes of display and advertising.

Here is part of the definition of a model from my trusty Webster's NewWorld Dictionary Second College Edition (1986):

4. a) a person who poses for an artist or photographer; b) any person or thing serving as a subject for an artist or writer; c) a person, esp. a woman, employed to display clothes by wearing them; mannequin.

Here is part of the defintion of a model from Oxford Dicitionary Online:

6) a person employed to display clothes by wearing them. 7) a person employed to pose for an artist.

So, it appears that the occupational title of model is not limited to people who are employed to display clothes or asscessories by wearing them.