Q:

Model View Controller. What is Model?

What is model ?
I am an ASP.Net WebForms developer.
I have been studying MVC for couple of days.
I can understand the concept of Controller and View but What is Model ?
Is it Data ?
Does it have to be with LINQ or we can use traditional stored procedures ?

A:

Is it Data ?

Generally it's data and behavior.  When you go about designing your model I'd suggest forgetting about "database" altogether.  The Domain Driven Design book has an excellent example of this.

Does it have to be with LINQ or we can use traditional stored
  procedures ?

Try and create your model to be persistent ignorant.  Lots of answer mention a database but ideally the model shouldn't have any knowledge of how it's persisted.  And in some cases some not all parts of the model will be persisted.  Look at the kigg source.  It shows a clear separation between the model and the persistence.  It shows implementing EF and Linq as two different options.
IMO, The ASP.NET MVC in Action books do a great job of laying out the different parts of MVC and discussing the different "models", ViewModel vs Entity Model, etc.
edit: Maybe the question should be, In (Domain driven design || Data driven design), what is the model?

