Every e-mail account or website on the Internet is hosted on a server. Each server is identified by a unique set of numbers called an IP address, for example,

However, as numbers are difficult to remember, IP addresses are associated with more readable addresses, called URLs or Internet addresses. A domain name is the part of a URL that appears between the penultimate and final dots. For example, in the URL http://www.europa.eu, the domain name is europa.

Each domain name has an extension, such as .eu, .com, .net, etc. These extensions, which appear after the final dot of a URL or Internet address, are called top-level domains (TLDs). In the case of the URL http://www.europa.eu, the extension of the domain name europa is .eu. TLDs are at the top of the hierarchy of the Domain Name System (DNS).

Generic TLDs (gTLDs) include .com, .net, and .int. There are also country-code top-level domains (ccTLDs), such as .es, .cz, .be, and .fr. Each TLD is managed by a so-called registry, a body appointed at national level (for ccTLDs) or by ICANN (for gTLDs) to run the top-level domain operations.