> An Availability Zone is one or more discrete data centers with separate and redundant power infrastructure, networking, and connectivity in an AWS Region. Availability Zones in a Region are meaningfully distant from each other, up to 60 miles (~100 km) to prevent correlated failures, but close enough to use synchronous replication with single-digit millisecond latency.

> https://docs.aws.amazon.com/whitepapers/latest/aws-fault-iso...

They are far enough apart that tornados, floods, and fires cannot simultaneously impact multiple.