There are 2 services you'll need for a functioning web site - a domain and a web hosting plan for it. Each time you type the domain in your browser, you see the content that is uploaded in the website hosting account, but if that domain address is not linked to such an account or to an e-mail service, it's parked. Put simply, the domain address is registered and you're its owner, but it does not have any content of its own. As a substitute, it can open either a pre-made “Under Construction / For Sale” page from the registrar company, or it can be directed to any other URL of your choice. The advantage of parking a domain is that you can keep it and be sure that no one else will take it. In the meantime, it's not going to occupy a slot for a hosted domain address in your account. You may also park domains if you have a .com, for instance, and you register domain names with other extensions such as .net, .org or country-code ones to direct them to the main site in order to protect a brand name.