In computer networking, a domain name is a name given to a collection of network devices that belong to a domain which is an administrative space managed according to some common characteristics of the members. For example, the computers of a corporate network running Windows NT services are said to belong to a domain (NT domain). In particular, the term domain name is best known in connection with the Internet where it describes the regions of administrative authority within the Domain Name System, the facility to locate resources on the Internet. This article is about Internet domain names.

Internet domain names are used in a variety of contexts for identification, reference, and access to Internet resources. They can appear as components of Web sites' Uniform Resource Locators (URL, 'Web-address'), e.g. www.wikipedia.org, electronic mail (e-mail) addresses after the customary '@' separator from the user's name, or as any other part of a syntax that describes an access method to a device or service in an IP network.

Domain names are created out of a naming space and methodology that was first defined by Paul Mockapetris in IETF publication RFC 882 and RFC 883 (1983) and used in the first expansion of the ARPANET, a predecessor of today's Internet. The model prescribes a tree-like structure of named nodes starting from an unnamed root node (cf. DNS root zone) that was only designated by a full stop (period, dot, "."). The complete domain name of each node is the string of names of nodes leading to the root node, each separated by a dot. The sequence is written from left to right with increasing order of scope, e.g., node-d.node-c.node-b.node-a. When the full name path of a node is specified, the domain name is said to be fully-qualified (cf. Fully qualified domain name). This condition is often, particularly in the technical aspects of DNS), indicated explicitly by appending a dot at the end of the name (to indicate the root domain).

The DNS methodology confers a unique name to every resource or service participating in the domain name system. This name is referred to as the domain name of a device or Internet host. However, not all nodes in the tree system denote a specific device, rather they are parent labels of an entire collection of subordinate nodes. Such nodes are the domains of the Internet. They represent the spaces of autonomy that are delegated by a group of service providers, called domain name registrars.

These registrars are accredited by the Internet Corporation for Assigned Names and Numbers (ICANN), the organization charged with overseeing the name and number systems of the Internet. In addition to IANA, each top-level domain (TLD) is maintained and serviced technically by a sponsoring organization, the TLD Registry. The registry is responsible for maintaining the database of names registered within the TLDs they administer. The registry receives registration information from each domain name registrar authorized to assign names in the corresponding TLD and publishes the information using a special service, the whois protocol.