False Domain Names - Directory Listings - Free Hosting
This is not a real domain name, it is a directory - and you should try to avoid it.
These URLs are not desirable, especially for companies. Try to avoid them if you can afford to register a domain. Typically these are more commonly used for personal sites and free sites provided by your ISP, you may have seen www .primarydomain.com/~username as a common address, this is just another way to share a single domain and provide users their own address.
Open competition in domain name registration has brought about a dramatic decrease in pricing so domain sharing is far less common since people can register their own domains for only $8.95 per year.