Domain name is a string consisting of numbers, hyphens and characters that is used for addressing purposes on the internet. In 2014, the number of active domains reached 271 million. The domain name consists of a string of your choice and an extension (e.g. domain.tips: domain is the string and .tips is the extension). The extension is a generic top-level domain (TLDs like .com, .net), country code top-level domain (ccTLDs like .hu, .de, .us), new generic top-level domain (nTLDs like .tips, .club, .guru).
A domain can be further divided to subdomains e.g. translate.google.com is a subdomain of google.com. A widely used subdomain is www. The full domain name may not exceed 253 ASCII characters, however, some registries have shorter limits.
The official list of top-level domains is processed and maintained by IANA (Internet Assigned Numbers Authority).