A domain name is a human-readable name used to identify a location or namespace on the Internet, most visibly for websites, email services and other networked services. Examples include example.com, bbc.co.uk and mail.example.org. Domain names provide a layer of abstraction above numerical IP addresses, allowing people and applications to use stable names instead of remembering network addresses. The Domain Name System maps domain names to DNS records, which can contain IP addresses and many other types of information.
A domain name is hierarchical rather than merely a single arbitrary label. In www.example.com, the labels are separated by dots, with com being the top-level domain, example being the registrable domain in this context, and www commonly being a subdomain. Domain names can identify different services or organisational namespaces, but owning a domain name does not automatically mean owning every hostname beneath it in an absolute sense; control depends on the relevant DNS and registration arrangements.
Domain names are organised into a hierarchical namespace administered through the Domain Name System. The rightmost label is the highest level in an ordinary fully qualified domain name, so com is above example.com, which is above www.example.com. At the top of the DNS hierarchy are the root servers and the root zone, below which are top-level domains such as .com, .org, .uk and many others.
A domain such as example.com can contain records for the domain itself and for subordinate names such as www.example.com, api.example.com and mail.example.com. The term domain can therefore refer to different levels of the DNS hierarchy depending on context. A registrable domain is the portion that a customer can generally register through a registrar, but the boundary varies with public suffix structures. For example, a registrant might register example.co.uk, whereas co.uk itself is a public suffix rather than an ordinary registrable domain for that customer.
Domain-name registration is the process by which a person, organisation or other eligible entity obtains control over a domain name for a specified registration period through a registrar or reseller operating within the relevant registry system. Registrars interact with registries that maintain authoritative records for particular top-level domains.
Registration does not generally mean that the registrant owns the name as permanent physical property; it provides contractual rights to use and manage the domain for the registered period, subject to the rules of the applicable registry and registrar. Registrants normally configure authoritative nameservers, which publish DNS information for their domain.
A domain can then have records such as A and AAAA records for web servers, MX records for email, CNAME records for aliases, TXT records for verification or policy information, and other specialised records. Domain registration and website hosting are separate services, so a registered domain does not inherently include a website, server, email service or hosting account.
Domain names can contain several types of labels with distinct functions. A hostname such as www.example.com may be used by a web server, while mail.example.com might identify an email-related system and api.example.com might identify an application programming interface. These names can point to the same IP address, different IP addresses, or other DNS names. A subdomain is normally created under the administrative control of the parent domain and can be delegated further.
Domain names are case-insensitive in DNS, so Example.COM and example.com represent the same DNS name, although applications and URLs can have additional case-sensitive semantics in their paths. DNS labels have length and character restrictions, and internationalised domain names allow users to represent domain labels using many writing systems. Such names are converted into an ASCII-compatible representation for DNS protocols, allowing the global domain-name system to support a much broader range of scripts.
Domain names serve practical purposes beyond replacing IP addresses. They provide a stable naming layer that allows an organisation to change hosting providers, servers or network addresses without requiring users to learn a new name. DNS can return multiple addresses for one domain, support aliases, distribute traffic and direct different services to different infrastructure. Large websites may use geographically distributed DNS responses, load-balancing systems, content delivery networks and cloud platforms while retaining a consistent public domain.
Domain names are also central to email because MX records specify the mail-handling hosts for a domain. Certificates used by HTTPS are normally issued for domain names or related identifiers, allowing browsers to authenticate the hostname to which they connect. Consequently, a domain name can become a central identity and infrastructure component for a website, organisation or online service, rather than simply being a convenient label.
Domain names are different from URLs, hostnames and IP addresses, although the concepts are closely connected. example.com can be a domain name and can also function as a DNS name, but a complete URL such as https://www.example.com/news contains much more information, including a scheme and path. www.example.com can be described as a hostname when it identifies a network host or service, while example.com can be the registered domain beneath which that hostname exists.
An IP address such as 203.0.113.10 identifies a network interface or endpoint at the Internet Protocol layer rather than providing a human-oriented hierarchical name. DNS provides the mechanism that relates names to addresses and other records. These distinctions matter because changing a DNS record can change where a hostname resolves without changing the domain registration itself, while changing a URL path can change the requested application resource without changing the domain or host.
Domain names have commercial, administrative and security implications. Names are registered under policies established for individual top-level domains, and disputes can arise when a name resembles a trademark or is registered in bad faith. Domain-name abuse can include phishing, impersonation, malware distribution and deceptive registrations. DNS Security Extensions can provide cryptographic validation of DNS data, while certificate authorities use domain-control validation when issuing many TLS certificates.
Domain privacy services may reduce public exposure of some registrant contact information where permitted, but they do not make domain ownership inherently anonymous to registries or law-enforcement processes. Domain expiration can also have serious consequences: if a registration is not renewed and passes applicable grace and deletion periods, another party may eventually be able to register the name.
The domain-name system emerged from the need to make Internet hosts easier to identify than through numerical addresses and to replace the increasingly impractical single hosts-file approach. The DNS was introduced in the 1980s as a distributed, hierarchical naming system. Its architecture separates administration of different portions of the namespace and allows each domain's authoritative servers to manage its own records.
The introduction of generic and country-code top-level domains created the broad structure familiar today, while later expansion introduced many additional top-level domains and internationalised domain names. The result is a globally distributed naming system in which domain names provide a human-oriented layer over Internet addressing and service discovery. Understanding a domain therefore requires understanding registration, DNS delegation, authoritative nameservers, hierarchy, hostnames and the relationship between names and the network services to which they resolve.
