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An FQDN (Fully Qualified Domain Name) is a complete domain name that uniquely identifies a specific host in DNS, including all domain levels. For example, mail.nic.ua is an FQDN, where mail is the host name (or subdomain), nic is the second-level domain, and .ua is the top-level domain.
In simple terms, an FQDN is the full address of a name in the DNS hierarchy, not just the “main domain.” This format is used in DNS settings, email services, SSL certificates, server configuration, and network applications when an exact, unambiguous host name is required.
An FQDN is the full name of a host or domain, including all levels. For example, mail.example.com is an FQDN because it includes the host name, the main domain, and the domain extension.
A regular domain often refers to just the base name (for example, example.com), while an FQDN is a complete name that includes a specific host or subdomain (for example, www.example.com or mail.example.com). FQDNs are more precise in technical configurations.
FQDNs are used in DNS records, email settings (MX, SMTP), SSL/TLS certificates, server configuration, cloud services, and network applications — anywhere an exact host name must be specified.