What is Nano!?

The title pretty much sums it up, what the heck is this Nano? I hear it EVERYWHERE, i see it on stories, i read about it in journals, i see it in comments, i see people gloating about it, i see people talking about other people gloating about it, i see people whining about how they'll never reach their nano goal. Apparently this Nano thing is popular, so can anyone tell me WHAT THE HECK IS NANO!?

Thankyou for your time *chinese bow*

PLEASE TELL ME, it's driving me insane! The feeling of not knowing generally drives me insane, so this is driving me insane!