A domain name is the alphabetic equivalent of an address on the Internet. The name actually translates to a unique series of numbers (Internet Protocol Address).
Domain names are used instead of the IP address primarily because people can more easily remember a word rather than a long set of numbers. The other reason is that a domain can be moved to a new server, that will have a new IP, but the name remains the same. The DNS (Domain Name System) server translates domain names into the IP addresses.
The most popular TLDs (such as .com, .net, .org, .info) are available for private registration through Datamerc by request. Typical cost is $20.00 per year.