What is Model's actuall purpose in ASP.NET MVC or MVC architecture

I'm in confusion and even unclear about Model term in MVC architecture. I understand View and Controller. But in case of Model I'm not able to understand it's purpose. I went through many documentation some says Model consists of Data Representation and Business logic or algorithm and some says its just data representation in some use synonyms like Active Record and Data Transfer Object.

I've been using ASP.NET MVC for a past few months, where we use term ViewModel. We create a separate class library maned it as ViewModel and which contains classes with properties (such as UserViewModel.cs which really represents data) and Agents which contains business logic. With this overall mixing up I'm not able to understand what actually model in the MVC architecture.

Sorry for posting a duplicate question but whatever I found in SO did not clear me the concept. Could any one please help me.