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An internet domain name is a human-readable name in the Domain Name System (DNS) that identifies a node in DNS’s hierarchy. For example, www.icann.org is a domain name: its labels, separated by dots, identify a position in the name-space tree. DNS can associate information such as a host address with that name, but the name itself is not a website, a web address, or the DNS lookup system.
How a domain name is structured
DNS is organized as a hierarchy, often described as a tree. Each point in that tree is a node with a label. A domain name is the sequence of labels along the path from a particular node toward the root. In ordinary writing, the most specific label comes first, and dots show the boundaries between labels. RFC 1034 describes a domain name as “the list of the labels on the path from the node to the root of the tree.”
In whois.icann.org, whois is the third-level label, icann is the second-level label, and org is the top-level domain (TLD). A name below another name in the hierarchy is commonly called a subdomain, so whois.icann.org is a subdomain of icann.org. The root is the top of the DNS hierarchy; it is not normally displayed as a trailing dot in everyday use.
“Domain” and “domain name” are closely related, but they are not quite the same term. A domain is the part of the name-space at or below the node identified by a domain name; the domain name is the label sequence that identifies that node.
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Domain name, DNS, website, and URL: what is the difference?
| Term | What it is | What it does |
|---|---|---|
| Domain name | A hierarchical name identifying a node in DNS, such as example.com. |
Provides a name that DNS queries can use to request associated resource information. |
| DNS | The naming system and protocols, including components such as name servers and resolvers. | Processes queries for names and returns associated resource data, which can include host address information. |
| Website or URL | A website is a service; a URL is a locator that can include a domain name. | A website may be made available using a domain name, but registering the name does not create the website or its URL. |
A registered name can be configured for a website, email, or other services. Those services require their own hosting or infrastructure and configuration. Registration by itself does not make a site load or provide working email.
What registration and delegation mean
Registering a domain name gives a name to a realm in DNS; it does not mean that one person or organization administers every level of the hierarchy. Authority can be delegated downward, allowing different parties to manage different levels or branches. For example, the root zone and TLDs are part of a hierarchy in which responsibility is delegated. This arrangement lets administration be distributed while names remain part of the same DNS tree.
What is a fully qualified domain name?
A fully qualified domain name (FQDN) gives the complete path of labels to the DNS root, identifying a name’s exact position in the hierarchy. In everyday contexts, people often use “domain name” for a name such as www.icann.org without spelling out the root explicitly. The important distinction is that an FQDN denotes the full hierarchical name, rather than only a portion of it.
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People can use a memorable name instead of needing to enter or remember numeric network details. DNS provides the lookup mechanism: a resolver asks for particular resource information associated with a name, and DNS infrastructure can return the relevant data. The domain name identifies a node; DNS is the system that answers queries about it. That is why buying or registering a name is only one step toward making a website or email address work.
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