What is a model? It is the M of the MVC pattern.

What does it do? It separates domain logic from the presentation, isolating application logic.

A model is generally an access point to the database, and more specifically, to a certain table in the database. By default, each model uses the table who's name is plural of its own, i.e. a 'User' model uses the 'users' table. Models can also contain data validation rules, association information, and methods specific to the table it uses.