a domain name

A domain name is the human-friendly name of something on the Internet, written as labels separated by dots — for example www.example.com. Think of it like a postal address read in an unusual order: rightmost first. The label on the far right (.com) is the broadest region; each label to the left narrows it down, until the leftmost label (www) names a specific host inside example.com. Just as a postal address goes country, city, street, house, a domain name goes from general (the right) to specific (the left).

Read precisely, the dots mark the levels of a tree. In www.example.com, com is a top-level domain, example.com is the second-level domain that an organization registers, and www is a subdomain or host label that the organization defines for itself. A name that spells out every level all the way up to the unnamed root is called a fully qualified domain name, and is sometimes written with a trailing dot (www.example.com.) to show it is complete. Labels are case-insensitive (Example.com equals example.com), each label is at most 63 characters, and the whole name is at most 255 characters.

Why it matters: the domain name is the stable, memorable identity you give out — on business cards, in links, in email addresses — while the numeric IP address behind it can change freely. That separation is powerful: a company can move its website to a new server with a new IP and keep the same domain name, so nobody has to update their bookmarks. A common misconception is that a domain name is the website; it is really just the name that DNS resolves into the address where the website currently lives.