What is Zone?
A zone is different whether you are talking about audio/video or security.
Each device on a wireless security system is its own zone. On hardwired security systems you may have many similar devices on one zone. For instance, every window contact in the living room may be programmed on the same zone. Zones are used to identify which alarm device triggered the alarm event to occur, so that the central station operators can provide location information to the responding authorities.
Zone is an audio zone. A set of speakers that can be individually controlled from other audio zones. Usually a Home Theater would be Zone 1, and a Patio or Bedroom can be Zone 2 on a multi-zone A/V receiver.