The Domain Name System (DNS) is a hierarchical, distributed global database, most commonly used for mapping hostnames to their respective IP addresses. It is defined in RFC 1034 and RFC 1035, and numerous updates thereof.

A domain name is a sequence of labels separated by the period character (.). Each label can have a maximum of 63 characters, and a domain name can have a maximum of 255 characters.

The DNS is often described as a tree structure, with the "root zone" at the top, the Top Level Domains (TLDs) e.g. com, uk, etc below that, etc. Within a domain name the labels are shown in a "little endian" order with the leaf node label appearing left-most, and the TLD appearing right-most. If a trailing period appears after the TLD then the name is said to be a Fully Qualified Domain Name, where the trailing period represents the root zone itself.