Domain Name Server Hierarchy. A - The host address associated with the domain name. In turn the root zone file contains resource records for the authoritative servers of all TLDs.
The second-level domain name is open to the public for customisation. The hierarchical Domain Name System for class Internet organized into zones each served by a name server. It is always combined with at least a second-level domain name.
A domain name is an identification string that defines a realm of administrative autonomy authority or control within the Internet.
The DNS hierarchy is comprised of the following elements. It is always combined with at least a second-level domain name. 1 Root Level 2 Top Level Domains 3 Second Level Domains 4 Sub-Domain 5 Host. Specific servers are designated as authoritative for portions of the name space.