The architecture is best described as High availability because running the web tier across three Availability Zones within a single AWS Region improves resilience and reduces single points of failure.

Placing instances in multiple Availability Zones allows traffic and workloads to fail over when one zone has problems and lets load be balanced across zones to maintain uptime, which is the core goal of High availability.

Elasticity refers to automatically scaling capacity up or down in response to demand and does not by itself describe distributing instances across Availability Zones for redundancy.

Global footprint implies deployment across multiple Regions or the use of global edge locations and is not achieved by using multiple AZs within one Region.

Security posture relates to protective controls and compliance and does not describe the redundancy or uptime benefits provided by a multi-AZ design.

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