Knowledgebase

A Top Level Domain (TLD) is the suffix that is attached to the end of a domain name. For instance, in the domain name mycompany.com, ".com" is the TLD. 
There are two types of top-level domains: global and country code. Global Top Level Domains (gTLD) were created to be used by the Internet public, while country code Top Level Domains (ccTLD) were created to be used by each individual country, as they deem necessary. Some of the global Top Level Domains are- .com .net .org .edu .mil .gov Some of the country code Top Level Domains are: .co.in (India) .co.au (Australia); .cx (Christmas Islands) .co.uk (United Kingdom)

Refer http://www.internic.net/faqs/new-tlds.html for more details