Q:

In 3 minutes, What is Reflection? 

Many .Net interview question lists (including the good ones) contain the question: "What is Reflection?".  I was recently asked to answer this in the context of a 5 question, technical test designed to be completed in 15 minutes on a sheet of blank paper handed to me in a cafeteria.  My answer went along the lines of "Reflection allows you to discover the Methods, Properties and Fields of any object at runtime".  In retrospect, my answer explains how you can use reflection, but it does not explain what reflection is.  In my view, my answer was sufficient to convey that I understand what reflection is for but didn't go so far as to explain what reflection is. 
So please, in the context of .Net, in your own concise words, define what Reflection is.  Don't spend more than three minutes answering.  Don't refer to the .Net documentation, we've all seen it. 

A:

Reflection is the ability to query and interact with the type system in a dynamic way.  

A:

a form of introspection i.e. the ability to write code that queries code

A:

Reflection is the CLR's awareness of code-level objects such class names, methods, etc.  that is exposed via an API, namely System. Reflection, which allows a developer to leverage the runtime's cognizance of this information in their code. 
Rule violation: I've edited this answer from its original form for the sake of accuracy.