A domain name is an identification label that defines a realm of administrative autonomy, authority, or control in the Internet. Domain names are hostnames that identify Internet Protocol (IP) resources such as web sites. Domain names are formed by the rules and procedures of the Domain Name System (DNS).
Domain names are used in various networking contexts and application-specific naming and addressing purposes. They are organized in subordinate levels (subdomains) of the DNS root domain, which is nameless. The first-level set of domain names are the top-level domains
Domain name space
The domain name space consists of a tree of domain names. Each node in the tree holds information associated with the domain name. The tree sub-divides into zones beginning at the root zone.
The top-level domains (TLDs) are the highest level of domain names of the Internet. They form the DNS root zone of the hierarchical Domain Name System. Every domain name ends in a top-level or first-level domain label.