A domain name is an identification string that defines a realm of administrative autonomy, authority or control within the Internet. Domain names are formed by the rules and procedures of the Domain Name System (DNS). Any name registered in the DNS is a domain name.

List of Internet top-level domains

This is a list of Internet top-level domains (TLDs). A top-level domain is a domain name in the Domain Name System that is a direct subdomain of the DNS root zone. The official list of all top-level domains is maintained by the Internet Assigned Numbers Authority (IANA). In an initiative to expand the domain name space, IANA is considering approval of several proposed top-level domains. As of February 2015, the root domain contains 810 top-level domains, while a few have been retired and are no longer functional.

Original top-level domains:- TLDs & generic top-level domains (gTLDs)

.com ( Commercial Operated by Verisign ) - This is an open TLD; any person or entity is permitted to register.
.org ( Organization Operated by Public Interest Registry) - This is an open TLD; any person or entity is permitted to register.
.net ( Network Operated by Verisign) - This is an open TLD; any person or entity is permitted to register.
.int ( International Organizations Operated by Internet Assigned Numbers Authority) - The .int TLD is strictly limited to organizations, offices, and programs which are endorsed by a treaty between two or more nations.
.edu ( U.S. Higher Education Operated by Educause (via Verisign) ) - The .edu TLD is limited to specific educational institutions
.gov ( U.S. National & State Government Agencies Operated by General Services Administration (via Verisign)) - he .gov TLD is limited to governmental entities and agencies in the U.S.
.mil ( U.S. Military - Operated by United States Department of Defense ) - The .mil TLD is limited to use by the United States military.

generic top-level domains (gTLDs) :-

Generic TLD's include .com, .net, .biz, .org and .info - these can be registered by anyone.

International Popular Domain Extensions:

.com ( Commercial
.org ( Organization
.net ( Network )
.biz ( Businesses )
.info( Informational )
.in ( India )
.us ( United States of America )
.uk ( United Kingdom )

Country - top-level domains ( ccTLDs )

.in ( India )
.us ( United States of America )
.za ( South Africa )
.uk ( United Kingdom )
.sa ( Saudi Arabia )
.ru ( Russia & also .su )
.ph ( Philippines )
.nz ( New Zealand )
.mx ( Mexico )
.jp ( Japan )
.it ( Italy )
.hk ( Hong Kong )
.fr ( France )
.bz ( Belize )
.br ( Brazil )
.au ( Australia )
.ae ( United Arab Emirates )
.ac ( Ascension Island )
.af ( Afghanistan )
.ca ( Canada )