Top-level domain
An Internet domain name is a string of typographic characters used to describe the location of a specific individual, business, computer, or piece of information online. Formally known as the Uniform Resource Locator or URL, it is often considered to be the address of a certain World Wide Web site. Obtaining an Internet domain name is a vital step for small businesses hoping to establish a presence on the Internet. "To be a major league team in the Internet game, your business will want a domain name of its own, " Vince Emery wrote in How to Grow Your Business on the Internet. "These valuable intellectual assets … make the difference in your image between Internet pro and fumbling amateur. Your domain name is more than your address. It tells the world who you are and what you are.
A typical domain name consists of several parts. As an example, consider an auto parts business with the domainwww.spareparts.com. The letters www. before the domain name mean that what follows describes the location of a site on the World Wide Web. The last two or three letters of a URL are known as its top-level domain. About 250 top-level domains existed on the Internet as of the year 2000. 
Some of the most common top-level domains include .com, which usually indicates a business or commercial site; .org, which generally describes a nonprofit, charity, or cultural organization site; .gov, which indicates a governmental site; and .net, which is most often used by network-related businesses. Other common top-level domains are country codes, like .us for United States and .au for Australia. Small businesses can put as many subdomains as needed in front of their domain names. For example, the customer service department of the aforementioned auto parts business might be designated aswww.service.spareparts.com.
Internet domain names are fairly easy and inexpensive to obtain. The process of registering a domain name involves searching to see if the desired name is already taken, filling out a form online, and paying a fee of $100 or so. But small businesses may find it exceedingly difficult to secure the exact domain name they want. As Jacqueline Emigh noted in Computer-world, the supply of available domain names is dwindling rapidly, particularly in the popular .com toplevel domain. In some cases, the best domain names are simply already being used by other individuals or firms. Some larger businesses will register several different domain names in case they might be needed in the future, or in order to protect themselves against competing sites. But in other cases, the best domain names are held by cybersquatters or cyberpirates. These individuals register a number of domain names that are likely to be coveted by businesses in hopes of selling them in the future for a significant profit. The U.S. government and several international authorities are beginning to crack down on the activities of cybersquatters.
A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System of theInternet. The top-level domain names are installed in the root zone of the name space. For all domains in lower levels, it is the last part of the domain name, that is, the last label of a fully qualified domain name. For example, in the domain name www.example.com, the top-level domain is com, or COM, as domain names are not case-sensitive. Management of most top-level domains is delegated to responsible organizations by the Internet Corporation for Assigned Names and Numbers (ICANN), which operates the Internet Assigned Numbers Authority (IANA) and is in charge of maintaining the DNS root zone.
Originally, the top-level domain space was organized into three main groups,^[1] Countries, Categories, andMultiorganizations. An additional temporary group consisted only of the initial DNS domain,^[2] arpa, intended for transitional purposes toward the stabilization of the domain name system.
Countries are designated in the Domain Name System by their two-letter ISO country code;^[3] there are exceptions, however (e.g., .uk). This group of domains is therefore commonly known as country-code top-level domains (ccTLD). Since 2009, countries with non-Latin based alphabets or scripting systems may apply for internationalized country code top-level domain names, which are displayed in end-user applications in their language-native script or alphabet, but use a Punycode-translated ASCII domain name in the Domain Name System.
The Categories group has become known as the generic top-level domains. Initially this group consisted of GOV, EDU,COM, MIL, ORG, and NET.
In the growth of the Internet, it became desirable to create additional generic top-level domains. Some of the initial domains' purposes were also generalized, modified, or assigned for maintenance to special organizations affiliated with the intended purpose.
As a result, IANA today distinguishes the following groups of top-level domains:[4
country-code top-level domains (ccTLD): Two letter domains established for countries or territories. With some historical exceptions, the code for any territory is the same as its two-letter ISO 3166 code.
internationalized country code top-level domains (IDN ccTLD).
generic top-level domains (gTLD): Top-level domains with three or more characters
unsponsored top-level domains: domains that operate directly under policies established by ICANN processes for the global Internet community.
sponsored top-level domains (sTLD): These domains are proposed and sponsored by private agencies or organizations that establish and enforce rules restricting the eligibility to use the TLD. Use is based on community theme concepts.
infrastructure top-level domain: This group consists of one domain, the Address and Routing Parameter Area(ARPA). It is managed by IANA on behalf of the Internet Engineering Task Force for various purposes specified in the Request for Comments publications.
In addition, a group of internationalized domain name (IDN) top-level domains has been installed under test for testing purposes in the IDN development process.