Final answer:
The term for the fully qualified domain name assigned to a cluster is known as the 'Cluster Name' or 'cluster's hostname,' which must be registered in the DNS to resolve to the cluster's primary IP address.
Step-by-step explanation:
The term used to specify the fully qualified domain name (FQDN) assigned to a cluster, which must have an entry in DNS that resolves to the cluster's primary IP address, is known as the Cluster Name or sometimes simply the cluster's hostname. When setting up a cluster, it's crucial to ensure that this name is correctly registered in the Domain Name System (DNS), allowing users and services to locate and communicate with the cluster using this name rather than an IP address. The process involves mapping the cluster's FQDN with the cluster's primary or virtual IP address so that when the FQDN is mentioned in a network request, DNS can guide the request to the correct server.