MVC stands for Model-View-Controller. Any application that separates it’s data access, business logic and user interface is called MVC. There can be two types of MVC: convention-based and configuration-based.
Example, cakePHP is convention-based, i.e. you just need to follow the instructions of the core system to get your module ready in just few lines. Magento is configuration-based, i.e. you need to specify each and every thing to your module’s config file in order to get it work.
Blocks - Each Block object will render a specific bit of HTML. Block objects do this through a combination of PHP code, and including PHP .phtml template files. Blocks objects are meant to interact with the Magento system to retrieve data from Models, while the phtml template files will produce the HTML needed for a page
Models - Magento offers an Object Relational Mapping (ORM) system. ORMs get you out of the business of writing SQL and allow you to manipulate a datastore purely through PHP code (and other core business logics)
For more Information Magento for Developers: Part 1 - Introduction to Magento