What is MVC?

Answer:

Most programmers know this, but interviewers will likely look for a deep understanding of MVC, and some explanation or examples on how/why/ when you used it. 

MVC - Model, View, Controller - is simply a way of organizing your code into 3 separate layers each with there own job. 

Model - Usually contains data access code and all of you business logic code. 
View - Contains markup/design code, generally html,xml, json. 
Controller - Usually contains very little code, just whatever is needed to call the Model code and render the View code.

http://www.symfony-project.org/book/1_0/02-exploring-symfony-s-code