The difference between virtual and abstract

I just found an interest explanation of  the difference between virtual and abstract class in C#. I think it is pretty easy to understand.

An abstract function cannot have functionality. You're basically saying, any child class MUST give their own version of this method, however, it's too general to even try to implement in the parent class.

A virtual function, is basically saying look, here's the functionality that may or may not be good enough for the child class. So if it is good enough, use this method, if not, then override me, and provide your own functionality.

Reference: http://stackoverflow.com/questions/391483/what-is-the-difference-between-an-abstract-function-and-a-virtual-function