Top Level Domain is the name, word, abbreviation that follows the dot (.) in an email address and a website address. Now there are newer top level domains and they are one of the highest domains in the internet hierarchial domain name service(DNS) of the internet. And the DNS Root Zone is “thee” highest level of DNS. The National Telecommunications and Information Administration, www.ntia.doc.gov/ which comes under the US Department of Commerece, has the ultimate authority over the DNS Root.  New TLD’s, in their ” creation-naming”, have become very generic, very ‘industry’-centric, ‘profession’-centric, ‘hobby-centric’ etc., and have the gTLD designation, ‘g’ for generic.  

Indirectly related….. http://www.myfoxny.com/story/26030623/professor-lawn-signs

You’ll remember when there were primarily only dot-com’s, dot net’s, dot-gov and dot-mil here in the US.  In case you’ve forgotten, ‘com’ means commercial, mil means military, net means network. DotCom is the most popular, most well known, and most easily remembered when an address is articulated.  ICANN,  www.ICANN.Com the Internet Corporation for Assigned Names and Numbers authority, is a US based manager / regulator who is in charge of maintiaing the root.

One of the reasons, in addition to making the internet domain more profession-centric, industry-centric, hobby-centric accomadating is simply basic math. It’s estimated that there are about 1 billion website, each with a unique address (unique domain). You’ll hopefully knew that when you type, for instance, www.Google.Com the user-friendly name, google.com is translated into the real address, which is a number….74.125.228.208, and you could type this octet number into your browser’s address field instead of the words www.google.com, (try it) and therefore by entering the numbers, your browser will load the Google Home Page.  Apparently aside from the basic math part, many entities and or person what the same exact web address, and first come / first served. So if www.MyWebSite.Com and www.MyWebSite.Net and www.MyWebSite.Org and www.MyWebSite.Biz etc are inuse, then allowing for new domains, alllows for others to get perhaps their 2nd choice name for their website, eg: www.MyWebSite.Management

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http://computer.howstuffworks.com/internet/basics/internet-infrastructure5.htm