What is a TLD (Top-Level Domain)?

A top-level domain (TLD) is the name at the highest level in the hierarchical Domain Name System of the Internet. The top-level domain names are installed in the root zone of the domain name space.

For example, in the URL http://MyTLD.com, the ".COM" is considered the top-level domain. Management of most top-level domains is delegated to responsible organizations by the Internet Corporation for Assigned Names and Numbers (ICANN), which operates the Internet Assigned Numbers Authority (IANA) and is in charge of maintaining the DNS root zone.

ICANN currently distinguishes the following groups of Top-Level Domains:

•   Infrastructure Top-Level Domain (ARPA)
•   Country-code Top-Level Domains (ccTLD)
•   Internationalized Top-Level Domains (IDNs)
•   Generic Top-Level Domains (gTLD)

Generic Top-Level Domains

Generic top-level domains (gTLDs) are extensions / suffixes with three or more characters that represent generic words, categories, regions, cultures or brands. These include:

• Unsponsored top-level domains: domains that operate directly under policies established by ICANN processes for the global Internet community.
• Sponsored top-level domains (sTLD): These community-based domains are sponsored by private agencies/organizations that establish & enforce rules restricting its eligibility to use the TLD.  
• Upcoming new gTLDs (generic, community, city or brand). 

There are currently 22 generic top-level domains:

• .aero: the air transport industry
• .asia: companies, organizations and individuals in the Asia-Pacific region
• .biz: business use
• .cat: catalan language/culture
• .com: commercial organizations
• .coop: cooperatives
• .edu: post-secondary accredited U.S educational establishments
• .gov: government entities within the United States
• .info: informational sites
• .int: international organizations established by treaty
• .jobs: employment-related sites
• .mil: U.S. military
• .mobi: sites catering to mobile devices
• .museum: museum
• .name: families and individuals
• .net: originally for network infrastructures, now unrestricted
• .org: originally for organizations not clearly falling within the other gTLDs
• .pro: certain professions
• .tel: single name space for Internet communications services
• .travel: travel agents, airlines, hoteliers, tourism bureaus
• .xxx: pornography

Internationalized Domain Names (IDNs)

An Internationalized Domain Name (IDN) is a domain name that uses at least one character different from the basic latin letters (a, b, c...,z) digits (0,1,2...,9) and the dash "-". Internationalized Domain Names in Applications (IDNA) is a mechanism for handling internationalized domain names in various applications online, such as browsers.

In the process of testing internationalized top-level domains, ICANN implemented a set of IDN top-level domains that are translations of the name example.test into each language's script.

Since the .test implementations ICANN launched the Fast-Track Program for introduction of new country-code Internationalized TLDs. Numerous countries participated in the program. A full, continously updated list can be found on ICANN's website here.

These are some resulting live examples with active websites: http://президент.рф (president in russian/cyrillic), http://правительство.рф (government in russian/cyrillic).

Country-Code Top-Level Domains (ccTLDs)

Country-code top-level domains (ccTLDs) are all two-character extensions representing countries and their corresponding ISO3166-1 list codes. Below is  the full list of all generic and country-code top-level domains. The two-character combinations are the country-codes.