# What is a domain? Definitions and examples A domain is a **globally unique and distinctive name** for a logically defined section of the internet, for example, a website. Domains appear in this form: `www.example.com`. Having to remember web server **IP addresses** in order to access web content is difficult and time-consuming for humans. This is why a user-friendly alternative was created: the domain. This is an alphanumeric method that makes it easier for people to access websites. ## What is a domain? A domain is an essential part of a Uniform Resource Locator (URL) and indicates where a web resource can be found within a hierarchically structured **domain name system (DNS)**. The name server is in charge of translating the domain into an IP address. Specialised web servers are then entrusted with **resolving IP addresses**. This process works in a similar way to a directory assistance service. A user writes the domain `www.example.com` into the browser’s search bar and a request is then sent to the corresponding name server. Upon arrival `www.example.com` is then retrieved from the database and the deposited IP address is transmitted to the browser. ## Domain structure and domain type examples A complete domain name is known as a **fully qualified domain name (FQDN)**. A FQDN states the exact position of a target computer within the tree hierarchy of the domain name system and is made up of two parts, which are the **host name** and the **domain name**. The following example is a fictitious mail server’s FQDN –`mailserver.example.com`. While `mailserver` represents the host name, `example.com` indicates the domain where the specific computer can be found. For server **host names** responsible for operating websites, the typical `www` is used – `www.example.com.`. Note that the fully qualified domain name is different to internet addresses in everyday use in that they end with a full stop. This is due to the **hierarchical structure of the domain name system** and as a result, domains are itemised starting from the highest level and ending with the root label. [![Image: FQDN using www.example.com. example](https://www.ionos.com/en-ie/digitalguide/fileadmin/_processed_/3/5/csm_fqdn-example_d7743a0c04.webp "FQDN using www.example.com. example")](https://www.ionos.com/en-ie/digitalguide/fileadmin/DigitalGuide/Schaubilder/fqdn-example.jpg) The Fully Qualified Domain Name consists of different types of domains. From right to left, the domain example structure is as follows: root label, top-level domain (TLD), second-level domain (SLD), and third-level domain. The FQND of `www.example.com.` even contains four sections. In principle, domains can contain further subdomains below the third-level domain. ### Root label The first level of the Domain Name System is called the root label, or null label. The root label of a FQDN is **defined as empty** and generally doesn’t appear to online users. Entries on name servers and resource records must, however, exist as complete FQDNs followed by a full stop after the top-level domain – `www.example.com.`. ### Top-level domain (TLD) Since the root domain is defined as empty, top-level domains represent the **highest level of name resolution**. TLDs are managed by network information centers (NIC). The tasks that an NIC has to perform include operating a name server and allocating second-level domains underneath the TLD. The IANA (Internet Assigned Numbers Authority), a department of the central internet management ICANN, differentiates between two main groups of top-level domains, which are generic TLDs like *.com* and *.net*, and country-specific TLDs (ccTLDs) like *.us* or *.co.uk*. Some of the generic TLDs are operated as sponsored top-level domains from special interest groups or businesses. Registering such a domain can be associated with special requirements or conditions. Since top-level domains appear as the last part of a domain, they are often referred to as ‘domain endings’. Regarding the example domain, the ending *.com* corresponds to the top-level domain. ### Second-level domain (SLD) A second-level domain is a *freely chosen name below a top-level domain*. An example is *example* in the namespace *com*. Allocating SLDs is always done in tandem with the superior TLD. An NIC-accredited private sector registrar is normally responsible for name allocation for business to customer purposes. Domains can be bought and registered here. ### Third-level domain Domains on the third level are known, of course, as third-level domains. In an FQDN these are placed in front of the second-level domain. By including a third-level domain, you can **define a sub-address**, which separates different sections from each other. Domain owners have the possibility to provide other landing pages, services, or servers. Common names for third-level domains are www for web services, *m* for mobile services, *mail*, *imap*, or *pop3* for mail servers as well as various country codes for language-specific services. A clear example is the online encyclopedia, Wikipedia. The site can be offered in different languages thanks to the third-level domain: [![Image: Comparison of different third-level domains from Wikipedia](https://www.ionos.com/en-ie/digitalguide/fileadmin/_processed_/b/1/csm_different-third-level-domains_10575b710e.webp "Comparison of different third-level domains from Wikipedia")](https://www.ionos.com/en-ie/digitalguide/fileadmin/DigitalGuide/Schaubilder/different-third-level-domains.jpg) Wikipedia uses different third-level domains for the different country versions. The English website can be accessed when the third-level domain *en* is used. By using *de* you will be directed to the German website. A third-level domain also offers companies the chance to show that they have branches in different locations and want to offer a regionally-targeted service or product on a separate website under the same second-level domain (e.g. the company name). Third-level domains are often referred to as ‘subdomains’. This term isn’t just limited to the third-level domains, though. This is a markdown version of: [https://www.ionos.com/en-ie/digitalguide/domains/domain-tips/what-is-a-domain/](https://www.ionos.com/en-ie/digitalguide/domains/domain-tips/what-is-a-domain/) for AI/LLM consumption.