From the introduction:
Zombie-World is a hack of Apocalypse World which was created by D. Vincent Baker. It also borrows from Dungeon-World, another hack written by Sage LaTorra and Adam Koebel.
In Zombie-World, players assume the role of Survivors who find themselves caught in the middle of an undead outbreak. How and why everything went to hell isn't important. Once the dead start walking, all that matters is arming yourself, finding a safe place to hunker down, and having enough supplies on hand to make it through this thing.