There are two services that you need for a working web site - a domain name plus a web hosting plan for it. When you type the domain in your web browser, you see the content that is uploaded within the hosting account, but if that domain address isn't linked to such an account or to an e-mail service, it's parked. In other words, the domain address is registered and you're its owner, but it lacks content of its own. Rather, it can open either a pre-made “Under Construction / For Sale” webpage from the registrar company, or it can be directed to some other URL of your choice. The advantage of parking a domain name is that you can keep it and be sure that nobody else is going to take it. Meanwhile, it will not take a slot for a hosted domain address in your account. You could also park domains if you have a .com, for instance, and you register domains with other extensions such as .net, .org or country-code ones to forward them to the main web site as a way to protect a brand name.