Domain name extensions and its restrictions

.com - Short for .commercial. Domain names with the .com extension are by far the most popular, and can be purchased by any individual or business.
.net- Short for .network, domains using this extension can be registered by anyone.
.org - Any individual or business may now register a .org domain name.
.us - the Internet country code top-level domain (ccTLD) for the United States. Now available to register anywhere in the world.
.info - domains are available to the general public.
.biz - The .BIZ domain can only be used for a "bona fide business or commercial use".

.co.uk
.org.uk
.me.uk
.com.tw - Taiwan's ccTLD. Any business or organization, worldwide, can register a .com.tw or .org.tw name.
.org.tw - Any business or organization, worldwide, can register a .com.tw or .org.tw domain name.
.idv.tw - Taiwan's ccTLD. Any business or organization, worldwide, can register a .com.tw or .org.tw name.

.ca - Canada's ccTLD. There are additional contact attributes required for the Canadian ccTLD.
.cn - China's ccTLD. Any business or organization, worldwide, can register a .CN name.
.name - Available to the general public.
.cc - Top level domain for the Cocos (Keeling) Islands. Anyone in the world can register a .cc domain for any purpose.
.tv - TV has a category of domain names called "Premium Names" which have a different pricing structure.
.bz - The country-coded Top Level Domain (ccTLD) for the country of Belize. Anyone in the world can register a .bz name.
.nu - The ccTLD for the country of Niue, these domains can be registered by anyone.
.ws - Western Samoa's ccTLD
.tm - are available to anyone within the International Community. .com.cn - China's ccTLD. Any business or organization, worldwide, can register a .CN name.
.net.cn - China's ccTLD. Any business or organization, worldwide, can register a .CN name.
.org.cn - China's ccTLD. Any business or organization, worldwide, can register a .CN name.
.de - Germany's ccTLD The administrative contact must have a street address or P.O. box within Germany.
.jp - Japanese address requirements. Multilingual names will not be supported.
.in - Top level domain for India. Anyone in the world can register a .in name.