IANA today distinguishes the following groups of top-level domains:
country-code top-level domains (ccTLD): Two letter domains established for countries or territories. With some historical exceptions, the code for any territory is the same as its two-letter ISO 3166 code.
internationalized country code top-level domains (IDN ccTLD): ccTLDs in non-Latin character sets (e.g., Arabic or Chinese).
Test IDN TLDs were installed under test for testing purposes in the IDN development process.
generic top-level domains (gTLD): Top-level domains with three or more characters
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 domains are proposed and sponsored by private agencies or organizations that establish and enforce rules restricting the eligibility to use the TLD. Use is based on community theme concepts.
infrastructure top-level domain: This group consists of one domain, the Address and Routing Parameter Area (ARPA). It is managed by IANA on behalf of the Internet Engineering Task Force for various purposes specified in the Request for Comments publications.
Countries are designated in the Domain Name System by their two-letter ISO country code; there are exceptions, however (e.g., .uk). This group of domains is therefore commonly known as country-code top-level domains (ccTLD). Since 2009, countries with non-Latin based alphabets or scripting systems may apply for internationalized country code top-level domain names, which are displayed in end-user applications in their language-native script or alphabet, but use a Punycode-translated ASCII domain name in the Domain Name System.
Generic top-level domains (formerly Categories) initially consisted of GOV, EDU, COM, MIL, ORG, and NET. More generic TLDs have been added, such as info.
The authoritative list of currently existing TLDs in the root zone is published at the IANA website at https://www.iana.org/domains/root/db/.