A domain name is an identification string that defines a realm of authority, or control in the Internet. 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. In general, a domain name represents an Internet Protocol (IP) resource, such as a personal computer used to access the Internet, a server computer hosting a web site, or the web site itself or any other service communicated via the Internet.

Domain name is basically divided 3 subordinates levels these are called sub domains. The first-level set of domain names are the top level domains example of these domains are com, net, and the country code top level domain etc. The second and the third level domain names are typically open for reservation by end-users that wish to connect local area networks to the Internet, create other publicly accessible Internet resources or run web sites. The registration of these domain names is usually administered by domain name registrars who sell their services to the public.

An important function of domain names is to provide easily recognizable and memorizable names to numerically addressed Internet resources. This abstraction allows any resource to be moved to a different physical location in the address topology of the network, globally or locally in an intranet. Such a move usually requires changing the IP address of a resource and the corresponding translation of this IP address to and from its domain name.

Domain name registration with a registrar does not confer any legal ownership of the domain name, only an exclusive right of use.

The rapid growth of the network made it impossible to maintain a centrally organized hostname registry and in 1983 the Domain Name System was introduced on the ARPANET and published by the Internet Engineering Task Force.

Today, the Internet Corporation for Assigned Names and Numbers manages the top-level development and architecture of the Internet domain name space. It authorizes domain name registrars, through which domain names may be registered and reassigned.

A domain name consists of one or more parts, technically called labels that are conventionally concatenated, and delimited by dots, such as example.com.

  • The right-most label conveys the top-level domain; for example, the domain name http://www.example.com belongs to the top-level domain com.
  • The hierarchy of domains descends from the right to the left label in the name; each label to the left specifies a subdivision, or sub domain of the domain to the right. For example: the label example specifies a node example.com as a subdomain of the com domain, and www is a label to create http://www.example.com, a subdomain of example.com. This tree of labels may consist of 127 levels.
  • A hostname is a domain name that has at least one associated IP address. However, other top-level domains, particularly country code top-level domains, may indeed have an IP address, and if so, they are also hostnames.
  • Hostnames impose restrictions on the characters allowed in the corresponding domain name. A valid hostname is also a valid domain name, but a valid domain name may not necessarily be valid as a hostname.

Few companies have offered low-cost, below-cost or even cost-free domain registrations with a variety of models adopted to recoup the costs to the provider. These usually require that domains be hosted on their website within a framework or portal that includes advertising wrapped around the domain holder's content, revenue from which allows the provider to recoup the costs.