Quoting from the docs [1]:

Each AZ can be multiple data centers (typically 3), and at full scale can be hundreds of thousands of servers. They are fully isolated partitions of the AWS Global Infrastructure. With their own power infrastructure, the AZs are physically separated by a meaningful distance, many kilometers, from any other AZ, although all are within 100 km (60 miles of each other).

All AZs are interconnected with high-bandwidth, low-latency networking, over fully redundant, dedicated metro fiber providing high-throughput, low-latency networking between AZs. The network performance is sufficient to accomplish synchronous replication between AZs.

1 - https://aws.amazon.com/about-aws/global-infrastructure/regio...