A domain name is alpha-numeric Internet address, formed by the name that you have chosen, and a TLD. A domain name is most often used to name a website (such as www.gandi.net) or an email address (firstname.lastname@example.org). In these examples, “gandi.net” is the domain name; “gandi” the chosen name and “net” the TLD.
A domain name (like gandi.net) is easier to remember than an IP address (such as 188.8.131.52). Moreover, the domain name does not change according to the place where your web or e-mail data is actually hosted: you can change your hosting company or your Internet access provider without having to change the name of your website or your e-mail address.
In terms of syntax, a domain name must contain less than 63 alphanumeric characters (no spaces); domain names are not case-sensitive.
The rules of the naming system are set forth by the trustee authorities (such as ICANN), the databases are centralized by the registries (such as Verisign for the .com TLD), and commercial and usual management are ensured by registrars like Gandi.