A parked domain address is one that is taken, however it's not linked to any other service - web or e mail hosting. Put simply, such a domain name won't open any actual content in case you type it inside a web browser, but nobody can take it as you've already registered it and you are its owner. The advantage of acquiring a domain and parking it afterwards is the fact that you will be able to keep it and not stress that someone else might register it in the meantime if, for instance, the site for it is not ready yet. You are able to set a short-term Under Construction page for a parked domain while you are working on your site, or forward it to some other web address - temporarily or permanently. The latter option can be used when you have already registered domain.com, for example, and you get domain.net and domain.org, in order to protect a brand name or a trademark. In this case, the .net and .org domain addresses can be parked and directed to the .com as you don't need separate sites for them.