One of the first things you think about when talking about a website is the domain name. For example, you have now visited the website of Prepaid Webhost by typing "www.prepaidwebhost.nl" in your browser. A domain name consists of three parts.
www (a subdomain)
prepaidwebhost (the name, also called the second level domain (SLD))
nl (the extension, also called the top level domain (TLD))