Take, for example, the URL or Domain name http://www.affcom.net

	http://	is the viewing protocol in this case the http translates to hyper text transfer protocol - other protocols include FTP (File Transfer Protocol), SMTP (Standard Mail Transfer Protocol) and NNTP (Network News Transfer Protocol)
	www	is the servername
	affcom.net	is the domain name
	net	is the top level domain

The .net as shown above is known as an extension or TLD (Top Level Domain). Commonly used extensions or TLD's are as follows:

.com	Commercial, but is commonly used for everything
.net	Internet administrative site, but is commonly used
.org	Organization
.info	Information
.biz	Business
.us	United States
.coop	Exclusively for Cooperatives
.name	Personal Web sites

Each country also has their own extension designation - ie. .ca=Canada, .uk=United Kingdom (Britain), .fi=Finland, etc. For a complete list click here.

Registering a URL. URLs, or to be exact, domain names, can be registered (purchased) on a yearly or multi-year basis. When you own a domain name, you are the unique owner of that particular web address. For example, if ThomasD registers the domain www.ThomasD.com, he is entitled to build a website at the address http://www.ThomasD.com, and may use a personalized email address such as Thomas@ThomasD.com.

So who owns unregistered domains? Several private, for-profit companies are under contract from ICANN (The Internet Corporation for Assigned Names and Numbers) to allocate domain names.