What Is the Harlem Shake?

For those of you who live under a rock or only on this blogging site, you may not have heard of this new YouTube sensation that people are calling the Harlem Shake. Apparently it's the biggest thing since Gangnam Style, but if I'm honest it only came on my radar when somebody at my uni did one in the SU as an election publicity stunt. From what I can gather it involves people randomly dancing around in weird and wonderful costumes, but other than that I don't understand how this became popular. I've combed through them all to find what I deem the best one, so if somebody could watch it and very kindly explain to me why it's so great, would be much appreciated please :)