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In the Domain Name System
Domain name system

The Domain Name System is a hierarchical naming system for computers, services, or any resource participating in the Internet. It associates various information with domain names assigned to such participants....
 (DNS) hierarchy, a subdomain is a domain
Domain name

The term domain name has multiple related meanings:* A hostname that identifies a computer or computers on the Internet. These names appear as a component of a Web site's Uniform Resource Locator, e.g....
 that is part of a larger domain. For example, "mail.example.com" and "calendar.example.com" are subdomains of the "example.com" domain, which in turn is a subdomain of the "com" top-level domain
Top-level domain

A top-level domain , sometimes referred to as a top-level domain name, is the last part of an domain name, that is, the group of letters that follow the final dot of any domain name....
 (TLD).

Note that "subdomain" expresses relative dependence, not absolute dependence: for example, wikipedia.org comprises a subdomain of the org domain, and en.wikipedia.org comprises a subdomain of the domain wikipedia.org.






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In the Domain Name System
Domain name system

The Domain Name System is a hierarchical naming system for computers, services, or any resource participating in the Internet. It associates various information with domain names assigned to such participants....
 (DNS) hierarchy, a subdomain is a domain
Domain name

The term domain name has multiple related meanings:* A hostname that identifies a computer or computers on the Internet. These names appear as a component of a Web site's Uniform Resource Locator, e.g....
 that is part of a larger domain. For example, "mail.example.com" and "calendar.example.com" are subdomains of the "example.com" domain, which in turn is a subdomain of the "com" top-level domain
Top-level domain

A top-level domain , sometimes referred to as a top-level domain name, is the last part of an domain name, that is, the group of letters that follow the final dot of any domain name....
 (TLD).

Note that "subdomain" expresses relative dependence, not absolute dependence: for example, wikipedia.org comprises a subdomain of the org domain, and en.wikipedia.org comprises a subdomain of the domain wikipedia.org. In theory, this subdivision can go down to 127 levels deep, and each DNS label can contain up to 63 characters, as long as the whole domain name does not exceed a total length of 255 characters. But in practice some domain registries
Domain name registry

A domain name registry, also called a Network Information Center , is part of the Domain Name System of the Internet which converts domain names to IP addresses....
 have shorter limits than that.

A subdomain is sometimes termed a vanity domain
Vanity domain

In the Domain Name System , a vanity domain is a domain name, often a subdomain, whose purpose is to express the individuality of the person on whose behalf it is registered....
, especially when it is a subdomain of an ISP's own domain aliased to an individual user account. However, the term "vanity domain" has other usages, discussed at that article.

Some websites use different subdomains to point to different server clusters. For example, www.example.com points to Server Cluster 1 or Datacentre 1, and www2.example.com points to Server Cluster 2 or Datacentre 2, etc.

Subdomains are commonly used by organizations that wish to assign a unique name to a particular department, function, or service related to the organization. For example, a university might assign "cs" to the computer science department, such that a number of hosts could be used inside that subdomain, such as mail.cs.example.edu or www.cs.example.edu.

Depending on application, a record inside a domain, or subdomain might refer to a Host name, or a service provided by a number of machines in a cluster.

See also

  • Domain name
    Domain name

    The term domain name has multiple related meanings:* A hostname that identifies a computer or computers on the Internet. These names appear as a component of a Web site's Uniform Resource Locator, e.g....
  • Hostname
    Hostname

    A hostname is the unique name by which a network-attached device is known on a computer network. The hostname is used to identify a particular host in various forms of electronic communication such as the World Wide Web, e-mail or Usenet....
  • Domain Name System
    Domain name system

    The Domain Name System is a hierarchical naming system for computers, services, or any resource participating in the Internet. It associates various information with domain names assigned to such participants....