So what exactly is a domain name?

What’s referred to as a website’s domain name is the part of the of the Web address that comes right before the top level domain (which is the .com, .org, .net, .us, etc.) together with the top level domain itself.

So for example the domain name in the following Web address, also known as a URL (universal resource locator), is marked in red:

http://www.exampledomainname.com/some-page-name.html

The domain name is the part you register and reserves your site’s name on the Web. Anything else in the Web address is configurable by your site or your Web server, and doesn’t require registration. (Anything but the http://, which is not actually a part of the address, but more on that later.)

Here’s a complete breakdown of the components of a URL:
http://www.exampledomainname.com/some-page-name.html?parameter1=test&parameter2=drive

The green part is what’s known as the the sub-domain.  In the early days of the Internet it used to designate a specific computer on a network, and when the World Wide Web developed, Web servers were then designated as www.  But today it just evolved to mean a separate location on the Internet, as many domains and sub-domains can be served by the same physical computer.

Since once a domain name is registered, sub-domains are completely under the control of the domain’s owner, sub-domains are often used as  a way to dish out addresses for multiple websites.

So for example, someone may register example.com, and then put up sites named site1.example.com, site2.example.com, site3.example.com, etc., having to register just one domain name called “example.com”.

Many site addresses start with a “www”, however they just mirror what’s in the higher level domain and are completely redundant, i.e. www.example.com shows exactly the same pages as example.com.  These days the www, is mostly a vestige form the early days of the Internet.  And once you set up a Web hosting account with any hosting company, www.yourdomain.com is made to automatically mirror yourdomain.com, so you don’t have to worry about it.

As discussed before, the purple part together with the orange part combine to form a Web site’s domain name. In relation to the top level domain, the purple part is a sub-domain as well.

The orange part of the address is the top level domain. You are probably familiar with the most common top level domains of .com, .org, and .net. Each top level domain may have a different authority controlling the registration of its sub-domains. Some top level domains are assigned to countries, such as .us to the USA and .il to Israel.

The blue part of the address is a specific page on the website. It may have a .html or .htm extension, but not necessarily so. It can also specify directories as in /this-is-a-directory/and-this-is-a-page.html.  Or it may not be there at all, in which case, the server is called upon to deliver some pre-configured default page.

The brown part of the address, which is separated from the page with a question mark, is the parameter list.  If present, it’s used to pass variables to the software that generates the Web page.  The blue and brown parts combined, i.e. the portion of the URL to the left of the top level domain, are called the URI (universal resource indicator).

And finally, the http:// just designates the protocol with which the entity pointed to by the address is to be interpreted. HTTP stands for hypertext transfer protocol and essentially means it’s a Web page. In a Web browser, http:// is almost always all you’ll see, however a URL is an Internet address, and since the Internet includes many protocols other than HTTP, the URL is not truly complete without it.