Reliability & Performance
Availability Zone
An isolated data center within a region, with its own power and networking, so failure in one zone doesn't take down the others.
An availability zone is an isolated data center inside a region, with independent power, cooling, and networking. A region typically contains several zones, close enough for fast connections between them but separated enough that a fire, flood, or power failure in one doesn't touch the others. They're the building block for surviving a data center outage without leaving the region.
The point of zones is failure isolation at a useful granularity. Spread your servers across two or three zones in a region and a single data center going dark becomes a non-event, because the load balancer routes around it and the database standby in another zone takes over. It's high availability without the latency cost of going fully multi-region.
Not every provider exposes zones as an explicit concept. The developer-focused hosts often abstract them away. Where they're available, spanning zones is the standard, affordable way to get real resilience, and it's usually cheaper and simpler than a full multi-region deployment.