Metagame
Metagame consists of the off-screen simulation of events and interactions of NPCs and Zombie between themselves and their environment. The metagame becomes concrete when the simulated characters and events come "on-screen."
For example, the gunshots heard and the helicopter passing overhead are metagame events. Currently however, the player can't find who fired the gun or where the helicopter went. The dead will still follow the sounds, sometimes passing (or eating) the player, originating from somewhere off-screen.
Helicopter Event
As of build 33, the Helicopter Event was added to the game as a physical object that is unable to be seen but can be heard. The helicopter can be heard overhead and, if the player is outside, will follow the player around leading hordes of zombies towards the player. If the player is inside or in a forest when the helicopter arrives and does not leave, the helicopter will not follow the player. However, if the player is spotted outside and the player hides from the helicopter by moving indoors (or into a forest), the helicopter will still hover overhead thus still attracting zombies. After approximately one hour of the helicopter being unable to find the player, it may leave and come back approximately one hour later.
Newer players are advised to stay indoors for the entire day of the helicopter event, as it can be unclear if the helicopter is returning and the large numbers of zombies that the helicopter attracts can be difficult to deal with. The event can be detrimental to players with secluded bases as it can very quickly lead large hordes to locations they wouldn't usually go to. Even if the player avoids being spotted by the helicopter, the helicopter will still cause zombies to migrate slightly, so beware.
The player can determine if the helicopter is coming on a given day by listening to the Automated Emergency Broadcast System which can be tuned to on a radio and listening for the phrase "Air activity detected". The channel for the AEBS is randomized, unlike other pre-set channels.
The helicopter can arrive on Day 6-9, from 9 AM to 7 PM. Once the helicopter arrives, it will attempt to find the player for 1-4 hours. On default settings, the helicopter will only come on one day. Sandbox settings can be adjusted to make the helicopter come every 6-9 days or every 10-15 days, at randomized times of day, for added challenge.
In multiplayer, the helicopter can switch between hunting various players, however in singleplayer mode the helicopter only has one target (you).
Gun Fire and Screams
Up to once a day, the player may hear gunfire or screams in the distance. It is not currently possible to locate the source of these "meta sounds", but they will cause zombies to migrate. The developers have indicated that in the future, these events may also trigger physical events on the map such as loot spawns.
Future Metagame
In the future, the metagame could involve complex interactive storylines, influenced by the environment, random events, NPCs, or the player. Most NPCs, however, would just be random survivors just trying to make their way. But certain NPCs would have storylines in which they make AI decisions and have scripts; the decisions and scripts would change depending on random chance or input from other NPCs, the environment, or even the player. For example, in the Kate and Bob story, the player could take the position of the raider. Presumably, the raider-player could threaten Kate, kill Bob (or do something else). In other words the player takes part in the storyline, becoming a participant in the script and thus changing the script, NPCs, and the metagame.