It's a guy in a suit with a DHS badge who shows up at your door and says "you need to drop off the Net right now or the terrorists will win". Or maybe it's a phone call, but over the phone it's hard to tell real cops from Elbonian pranksters.

Edit: I'm not joking; this is my understanding of how the system is supposed to work.

It's a term used to scare people. There won't actually be a physical switch to kill the internet.

If anything, it will be the authority to disconnect portions of the net. Probably by asking ISPs to cooperate.