Domain Levels Defined

Because the Internet uses numeric addresses, when you visit any site, such as Amazon.com, you are actually visiting a site identified as IP Address 176.32.103.205. Since computers are great at locating complex strings of numbers, each computer in a network is identified by its own numerical address. However, since people tend to remember letters and words more easily than a long string of numbers, a naming software called Domain Name Services (DNS) was developed to translate domain names to IP addresses. On the Internet, DNS resides on public and private servers.

Domain names follow a strict naming convention, utilizing a three-level hierarchy: root level, top level, and second level. Each part of the name is separated with a period, pronounced as "dot," when the domain name is said out loud.

1. Root-Level Domains: The root-level domain is the starting point in the hierarchy, such as the company's name or other chosen domain name, for example Amazon, or Yahoo.
2. Top-Level Domains: The Top-Level Domain (TLD) is the part of the URL that is to the right of the root domain. These TLD's are the dot-com, or dot-org extension we see so often in a web site's address. But, there are actually two types of top-level domains: original and country.

The following table lists the original domain names and the types of organizations to which they are assigned.

Country-level domains, the second kind of TLD, are called country code top-level domains (ccTLDs). They correspond to a country, territory, or other geographic location. Examples are .us (United States), .uk (United Kingdom), .de (Germany), and .jp (Japan). For example, a site whose address is www.artcrafts.uk is located in England (United Kingdom) because it uses a ccTLD of 'UK'. The list of valid domain names is constantly being revised. There is a Top level domain designated for the U.S., but it's seldom used because it would result in an extremely long URL. Perhaps you have seen such addresses as for a university, or local government. These long addresses contain references to the city, state, and nation. As the example shows, the .us domain is divided into subdomains; with one subdomain for each state and one for Washington, D.C. The state subdomains are divided into cities, counties, or other regional groupings.
For example, clv.oh.us is Cleveland, OH; sf.ca.us is San Francisco, CA.

A second-level domain name may be added to the left of the root domain. Second-level domain names can contain both hosts and other domains called subdomains. Host names identify a specific host server at the Internet address. For example, www is often used. Subdomains are phrases, or categories within the Internet address, for example, sports.yahoo.com. The following series of images illustrates how domains are assigned to a variety of sites: