Every computer on a network is identified with an IP (Internet Protocol) address, in the form of 123.123.123.123. This address is unique for every computer, and acts exactly like a street address in real life.

Since every website on the web is hosted on a computer with a unique IP address, you could, knowing the address, type that into your browser navigation bar and connect to the website in this way.

For instance, the IP address of CNN.com is http://157.166.224.25. If you enter that into your browser address bar, you will be taken to CNN's homepage.

The problem is these sets of four numbers are impersonal and difficult to remember, which led to the creation of the domain name system, or DNS. Essentially all a domain name is is a list of names and the IP address associated with it.

So when you type CNN.com, your Internet Service Provider's DNS server will look up that domain name in its list and see what IP address it is supposed to connect to.

It's basically a shorthand for IP addresses.