What is a top-level domain (TLD)?
A top-level domain is the part of the domain name located to the right of the dot (" . "). The most common TLDs are .com, .net and .org. Several new top-level domains have been added to the menu recently, including, .biz, .info, .name, and .ws. The top-level domains have certain guidelines attached, but are for the most part available to any registrant, anywhere in the world.
Exceptions are the restricted TLDs (rTLDs) - which include .aero, .biz, .edu, .mil, .museum, .name, and .pro - that require the registrant to represent a certain type of entity, or to belong to a certain community. The .name TLD is available strictly for individuals, while .edu is reserved for educational entities, such as universities or high schools.
Where appropriate, a top-level domain name can be of geographic significance and hence only available to registrants in the locale defined by the TLD. These are called country-code TLDs (ccTLDs) and include such top-level domains as .bz (Belize), .ca (Canada), .dk (Denmark), .ec (Ecuador), .ie (Republic of Ireland), .uk (United Kingdom), .us (United States), .zw (Zimbabwe) and ,in for (India).