Cupcakes and Muffins

So, I love to bake...I like the measuring and mixing and all that stuff. And I love the smell of fresh goodies coming out of the oven.
I don't bake from scratch but that's because I don't have to tools, I use box mixes and I have yet to have a complaint.
As I was walking through the backstage area at work tonight, I started thinking there are cupcakes and muffins, but what's the difference?
So, that's my question for the day, what is the difference between muffins and cupcakes? I tried to think about it. I use to think that cupcakes were more about chocolate, lemon, angelfood and icing and muffins were about blueberries, banana nut, bran and poppyseed. But now I'm not so sure...
I mean there are chocolate muffins aren't there? I can't really be sure about the different classification, so I'm asking you. What do you think is the difference between the two?