A domain name, like www.coolexample.com, is a lot like a street address for a house or business. Let's use the White House as an example. The street address, Plot 45 Kanjokya Street, is an exact location. You might not know the exact street address, but when you visit Kampala, you can tell your cabbie that you want to visit the the museum and still get there. This is how a domain name is used: It's an easy way to reach the exact location of a website without having to remember its numeric address.
A domain name consists of, at least, a top-level and a second-level domain. A top-level domain (TLD) is the part of the domain name located to the right of the dot ("."). The most common TLDs are .com, .net, and .org.
Many domains, also called extensions, can be registered by anyone, like .com, .net, and .org. A second-level domain (SLD) is the portion of the domain name that is located immediately to the left of the dot and domain name extension. For example, the SLD in coolexample.com is coolexample.
Advanced Domain Name Description: A domain name represents a physical point on the Internet — an IP address. The Internet Corporation for Assigned Names and Numbers (ICANN) governs coordination of the links between IP addresses and domain names across the Internet. With this standardized coordination, you can find websites on the Internet by entering domain names instead of IP addresses into your Web browser.