DayZ is an open world, multiplayer, survival, zombie, horror game. The game is developed by Bohemia Inteactive and based of the popular Arma 2: Combined Operation mod with the same name. The game is often referred as DayZ Standalone(DayZ SA). The original DayZ mod was created by Dean "Rocket" Hall, who also works for Bohemia Interactive. The map is 225 km^2 big and is based of a real life place in north Czech Republic which are representing a Soviet state.
The game takes place in a fictional post-apocalyptic Soviet state, where you have to fight zombies and interact with people by either shoot them, team up or just greet them, while you are gearing up to get the best loot.