top-level domain

A top-level domain (TLD) is the last part of an Internet domain name; that is, the letters which follow the final dot of any 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).The Internet Assigned Numbers Authority (IANA) currently classifies top-level domains into three types:country code top-level domains (ccTLD): Used by a country or a dependent territory. It is two letters long, for example .us for the United States.generic top-level domains (gTLD): Used (at least in theory) by a particular class of organizations (for example, .com for commercial organizations). It is three or more letters long. Most gTLDs are available for use worldwide, but for historical reasons .mil (military) and .gov (governmental) are restricted to use by the respective U.S. authorities. gTLDs are subclassified into sponsored top-level domains (sTLD), e.g. .aero, .coop and .museum, and unsponsored top-level domains (uTLD), e.g. .biz, .info, .name and .pro.infrastructure top-level domains (iTLD): The top-level domain .arpa is the only confirmed one. .root has been known to exist without reason.
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<networking> The last and most significant component of an Internet fully qualified domain name, the part after the last ".". For example, host wombat.doc.ic.ac.uk is in top-level domain "uk" (for United Kingdom).
Every other country has its own top-level domain, including ".us" for the U.S.A. Within the .us domain, there are subdomains for the fifty states, each generally with a name identical to the state's postal abbreviation. These are rarely used however. Within the .uk domain, there is a .ac.uk subdomain for academic sites and a .co.uk domain for commercial ones. Other top-level domains may be divided up in similar ways.
In the US and some other countries, the following top-level domains are used much more widely than the country code:
.com - commercial bodies .edu - educational institutions .gov - U. S. government .mil - U. S. armed services .net - network operators .org - other organisations
Since the rapid commercialisation of the Internet in the 1990s the ".com" domain has become particularly heavily populated with every company trying to register its company name as a subdomain of .com, e.g. "netscape.com" so as to make it easy for customers to guess or remember the URL of the comany's home page.
United Nations entities use the domain names of the countries where they are located. The UN headquarters facility in New York City, for example, is un.org.
Several new top-level domains are about to be added (Oct 1997): .nom - individual people .rec - recreational organisations .firm - businesses such as law, accounting, engineering .store - commercial retail companies .ent - entertainment facilities and organisations
(1997-10-08)