There are two separate services you'll need for a functioning web site - a domain name plus a website hosting plan for it. Any time you type the domain name in your web browser, you see the content that is uploaded in the hosting account, but if that domain is not linked to such an account or to an email service, it's parked. To put it differently, the domain address is registered and you're its owner, but it does not have any content of its own. Rather, it can open either a pre-made “Under Construction / For Sale” webpage from the registrar company, or it may be directed to some other URL of your choice. The main benefit of parking a domain is that you can keep it and ensure that no one else will take it. Meanwhile, it's not going to occupy a slot for a hosted domain inside your account. You can also park domains if you have a .com, for example, and you register domains with other extensions like .net, .org or country-code ones to direct them to the main web site so as to protect a brand name.