Availability Zones are discrete interconnected datacenters within the same geographic region
Definition
Availability Zones (or AZs) are discrete interconnected datacenters within a small geographic region that are designed to reduce failure domains. By isolating the core dependencies of a datacenter (power, networking, cooling, etc.), systems that are distributed over multiple AZs can be more fault tolerant, and can remain available even if an entire datacenter becomes unreachable.