In computer networking, a domain name is a name given to a collection of network devices that belong to a domain which is managed according to some common property of the members or within a common administrative boundary. In particular, the term is used to describe the regions of administrative authority within the Domain name system used for the Internet (cf. DNS zone).

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 prescribed 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 authorized and 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.

In this context a domain name is sometimes referred to as a 'product' sold by domain name registrars. However, the rules of assignment specify that no legal ownership is conferred with such transactions, only the right of exclusive use and the authority to the name space. Once assigned, a domain name becomes part of the pool of registered domain names and is no longer available for use by anyone else.

Colloquially, marketers incorrectly refer to domain names as "web addresses", however, a web address is actually a fully specified World-Wide Web resource locator, such as http://www.example.org, actually pointing to a web site.

New domain names are usually registered through the registrar for annual terms with a minimum of one year. The maximum length of prepaid registration is often 10 years, but varies depending on the policies of the sponsoring registry of the top-level domain under which registration is sought. Registration periods may be extended, usually at any time, until the end of a grace period after the registration expiration date.

Domain names may be transferred between parties or advertised for 'sale'. This is often called the "domain name aftermarket" (see below). After a domain name registration and the grace period expire, the domain name is either returned to the pool of available names, or receives special treatment by the registrars and could possibly end up in the 'aftermarket'.