what is a number model?

Since this is not my area of expertise, I searched Google under the key words "number model" to get these possible sources:

http://www.minet.uni-jena.de/~novak/model.html
http://72.14.253.104/search?q=cache:Jv_3THbD6vIJ:andean.kulture.org/owen/owen1993chapter2.pdf+%22number+model%22&hl=en&ct=clnk&cd=3&gl=us&client=safari

Here is a simple definition that I found:

"Definitions of number model on the Web:

A number sentence that models or fits the situation. An equation."

I hope this helps. Thanks for asking.