What is a DNS cluster?
DNS clustering is using multiple nameservers that share the same records, located in different geographic areas to serve your DNS records.
Why is using a DNS cluster beneficial?
Nameservers in different locations, using different providers, in different datacenters, and on different uplinks removes the DNS single point of failure issue with using a DNS server on your hosting machine. e.g. As long as one nameserver in the cluster is functional, then people can still find and load your website.