The correct choice is One or more discrete data centers within a single geographic location. An Availability Zone consists of one or more physically separate data centers that provide redundant power and networking inside the same location within an AWS Region.

Each Availability Zone is designed to be isolated from failures in other zones and to allow applications to run across multiple AZs for high availability. A Region contains multiple Availability Zones and those AZs are located close enough for low latency yet separated for resilience.

A collection of server racks housed across several locations is incorrect because an Availability Zone is confined to a single geographic location and is not spread across multiple separate locations.

A network of edge sites used for global content delivery is incorrect because that description matches Amazon CloudFront edge locations which serve content near users rather than provide isolated compute and storage capacity like an Availability Zone.

A group of data centers distributed across multiple cities is incorrect because that scope aligns with an AWS Region which groups multiple Availability Zones rather than the AZ itself.

Full AWS Practitioner Certification Question