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domain name

A name made of label One dot-separated part of a domain name, up to 63 characters long. Full definition separated by dots, such as example.org, that points to a place on the internet. The part at the far right is the top-level domain. People usually register the label just to its left through a registrar A company that registers domain names for customers with the registry. Full definition, for a set number of years.

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DNS and technical foundations

Updated on 5 min read

A domain name is the readable name, such as example.com, that people type to reach a website or that appears after the at sign in an email address. It is easier to remember than the numeric address of a computer, and it can stay the same when the server behind it changes.

What a domain name is, in plain words

The DNS Domain Name System The internet's directory that links domain names to computer addresses. Full definition works like the internet’s directory: you give it a name, and it returns the information stored for that name, such as the address of a web server or the servers that receive its mail.

Technically, a domain name is an ordered list of labels: the pieces of text between the dots.

The word is used loosely, as the IETF Internet Engineering Task Force The open body that writes internet standards such as DNS, EPP and RDAP. Full definition’s own terminology document notes. Engineers call any name in the DNS a domain name, including shop.example.com. In the domain industry, “a domain” usually means the name someone registered, such as example.com.

How a domain name is built: labels, levels and the dots

A domain name is read from right to left, from the most general part to the most specific:

  1. The root, the top of the DNS tree. Its label is empty, so it is normally invisible; strictly, it is the final dot of a name.
  2. The top-level domain (TLD top-level domain The last part of a domain name, after the final dot. Full definition), such as com or es. To the DNS, a TLD is simply one level below the root.
  3. The second-level domain The name directly left of the TLD, such as example in example.com. Full definition, the label just left of the TLD.
  4. The third level and any further levels.

In shop.example.com, com is the TLD, example the second level and shop the third.

Which level the public registers at is a matter of policy, not technology, and the name itself does not show it; outside sources such as the Public Suffix List A volunteer-maintained list of domain endings, used by software to tell where one owner's domain ends. Full definition record it. Under most TLDs it is the second level, but some ccTLD country code top-level domain A top-level domain for a country or territory, usually two letters long. Full definition use fixed second-level labels. For Spain, the national plan for .es (Order ITC/1542/2005) allows third-level names under .com.es, .nom.es and .org.es, which are open and assigned without prior checks, and under .gob.es and .edu.es, which are restricted (as of October 2026). In a name under .com.es, es is the TLD, com is a fixed second level, and the registrant The person or organization that holds a domain name registration. Full definition chooses the third-level label.

Which characters are allowed and how long a name can be

The DNS protocol itself only limits length. The familiar character rules come from the applications that use names (host names, email and the web) and from each registry The central database and system of a top-level domain, or loosely the organization that runs it. Full definition’s policy.

The traditional rule is LDH Letters, Digits, Hyphen The letters, digits and hyphen allowed in traditional domain name labels. Full definition: the ASCII American Standard Code for Information Interchange The basic set of English letters, digits and symbols that the DNS was built on. Full definition letters a to z, the digits 0 to 9 and the hyphen, with no hyphen at the start or end of a label. Labels with two hyphens in the third and fourth positions are reserved; those starting with xn– carry the ASCII form of an IDN Internationalized Domain Name A domain name written in local scripts or with accented letters. Full definition, a name with accented letters or a non-Latin script. Capital letters make no difference: Example.COM and example.com are the same name.

Each label can be up to 63 bytes. The whole name can be up to 255 bytes in the form the DNS stores, which also counts a length byte for each label and one for the root, so the written name is a little shorter.

Registries add their own rules. As of October 2026, .es allows the letters of the Spanish languages, digits and the hyphen; no hyphen first or last; no name starting with xn–; at least three characters at the second level and two at the third; and at most 63. Anyone planning a short or unusual name should check the current rules with the registry or their registrar.

Subdomains, the apex and the fully qualified name

Technically, a name is a subdomain A name created under a registered domain, like shop.example.com. Full definition of another when it ends with all of that name’s labels: shop.example.com is a subdomain of example.com, which is itself a subdomain of com. In everyday use, a subdomain is a name the holder creates under their registered domain, with no registry or registrar involved; www is one like any other.

The apex is the top of a zone, the name with nothing in front of it, such as example.com. The zone’s SOA record Start of Authority The record at the top of a DNS zone holding its serial number and timing settings. Full definition and NS record Name Server record A DNS record that lists the name servers responsible for a domain. Full definition live there.

An FQDN Fully Qualified Domain Name A complete domain name including every part up to the top-level domain. Full definition contains every label up to the root and, strictly, ends with the root’s dot, as in mail.example.net. with its final dot. In practice the dot is usually left out. It matters where software might otherwise add a local domain to a name.

What you actually own when you register a name

For gTLD generic top-level domain A top-level domain not tied to a country, run under ICANN contracts. Full definition, ICANN Internet Corporation for Assigned Names and Numbers The nonprofit that coordinates the global DNS and gTLD policy. Full definition’s contract with registrars does not speak of an owner. The RAA Registrar Accreditation Agreement The contract between ICANN and each accredited registrar. Full definition defines a “Registered Name” and its “Registered Name Holder”, whose rights and duties come from a registration Obtaining the right to use a domain name for a set period. Full definition agreement with an ICANN-accredited registrar, within the policies of the registrar, the registry and ICANN.

As of October 2026, ICANN’s page on registrant responsibilities says the holder must keep contact details accurate and current, answer the registrar within 15 days, keep payment details current if the name renews automatically, and accept sole responsibility for registering and using the name.

A registration lasts for a set term and must be renewed. Three roles are involved: the registry decides what goes into the TLD’s zone, the registrar acts as the go-between, and the registrant is the person or organization on whose behalf the name is registered. Not every registration goes through a registrar.

For ccTLDs, the rules come from each registry or from national law, such as the 2005 Order for .es. Whether a domain name counts as property is a legal question that depends on the country.

Domain name, URL, website and email address: the differences

In a web address, formally a uniform resource locator (URL), the domain name is only the host part; a path such as /news points to a page on that server. An email address has a local part, the at sign and a domain: editor@example.com uses example.com.

A website is content stored on a server; the domain name points to that server through DNS record One entry in a DNS zone, made of a name, a type, a TTL and data. Full definition. The same domain can serve a website, email, both or neither.

A domain hack A domain name that spells a word by using the TLD as part of it. Full definition is a name read across the dot, where the TLD completes a word: a word ending in ly can be split before those letters to use .ly. Domain hacks usually rely on country-code TLDs: as of October 2026, IANA Internet Assigned Numbers Authority The functions that coordinate the root zone, IP addresses and protocol numbers. Full definition lists .ly as the ccTLD of Libya and .me as that of Montenegro. That country’s registry rules still apply.

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