What's DayZ?

I've seen Tony and Justin playing this and the game does not look bad at all, I am a bit interested, but I do not know what the game is about, please tell me more about it and maybe a download link so I can play with you guys and do a triple LP's thingy magicy.
I've also realised that you have to move from city to city and find resources, I get the resource part, but why move from city to city? Zombies?
What else can you do on Dayz?

DayZ is a survival game with zombies. You have to move city to city because either other players will kill you, or you will run out of resources to gather. DayZ is not free to play, though. It is a mod for Arma 2 and Arma 2: OA.

Arma III Just came out, so Arma II just went down in price. The base game runs off Operation Arrowhead ( Arma II isn't needed, just the free version). All Arma II games went down in price with the recent release of Arma III. If you're looking to play DayZ, now is a good time to grab a copy.