A Fully Qualified Domain Name (or FQDN) is a complete and unambiguous domain name that specifies an exact location for an object in a Domain Name System (DNS) hierarchy. It specifies all domain levels, including the top-level domain and the root zone. Most domain names as used in the internet’s Uniform Resource Locators (or URL) are only partially qualified (but work just fine).
A fully qualified domain name can be interpreted only in one way – it is a completely unique address for one and only one location.
Each element of a FQDN refers to a domain level, and the elements of a FQDN are separated by periods. Technically, a FQDN will always end with a period as well – thus, for example, a mail server named mail under the domain somedomain.com would use the FQDN:
mail.somedomain.com.
Note that when entering a FQDN in DNS zone files the final period is required – however, on most other occasions where you are asked to enter the FQDN (such as when filling out your submission form for an SSL.com certificate) can safely leave off the terminal period. Most modern software, including ours, takes care of this for you.
