What the hell Is planking?

i don't get it, people talk about it on Facebook and stuff and I've seen some stuff on the news saying they busted another planker, BUT THEY NEVER HAVE THE DECENCY TO TELL US EHAT THE HELL PLANKING IS ALL ABOUT? I know you lie stiff n stuff but that's it, I mean how did it start & WHY do they do it? What's the big deal? Why is it the 'in' thing to do? Has everyone suddenly gone retarded?