Explain Class D amps to "non audiophile friends"

Hey folks, I was really enjoying the thread explaining class A amps to class B and AB, wheni was wondering where Class D comes in. I would love to be a snob and say its for my friends, but I have to admit I am doing the learning here! (I am not implying that the other guy who posted was asking the question for his benefit)

Thanks for your help!
Jeff