Merge pull request #300882 from PesalaPavan/patch-602377

(AzureCXP) fixes MicrosoftDocs/azure-docs#438834

Author: prmerger-automator[bot]

articles/reliability/availability-zones-overview.md

@@ -26,6 +26,10 @@ The following diagram shows several example Azure regions. Regions 1 and 2 suppo
 
 To see which regions support availability zones, see [List of Azure regions](regions-list.md).
 
+## What is the difference between a datacenter and an availability zone?
+
+An availability zone is a logical grouping of one or more physically separate datacenters within a region. Each availability zone is built in a way that if something goes wrong in one (like a power outage or network issue), the others keep working. A single datacenter doesn’t offer this level of protection on its own.
+
 <a name='zonal-and-zone-redundant-services'></a>
 ## Types of availability zone support