A Fully Qualified Domain Name is the complete name to specify a specific computer's location in the hierarchy of a complete domain.
For example there may be two groups within the Dnsjuice organization; sales and support. So we could use the sub-domains sales.dnsjuice.com and support.dnsjuice.com. If there was a specific system in the support subdomain, the FQDN for this computer would be host1.support.dnsjuice.com.
Old dnsjuice.com is the FQDN for the web server for the entire Dnsjuice organization. Whereas support.dnsjuice.com could be the FQDN for the web server for only the support department inside of the Dnsjuice organization.