James Read's Code, Containers & Cloud blog

A fault domain (or failure domain) is essentially a set of resources, or components that share a common point of failure. One example of this is an Azure Availability Zone, or your own single Data Center. Typical points of failure for a fault domain are power (with no backup generator), or cooling, or a datacenter is served by a single network connection. The term “fault domain” could theoretically be applied to smaller areas of an application architecture, like a single network, or a rack of servers, but this article considers a fault domain more from a cloud architecture definition.