In the Domain Name System (DNS) hierarchy, a second-level domain (SLD or 2LD) is a domain that is directly below a top-level domain (TLD). For example, in, example is the second-level domain of the .com TLD.

Second-level domains commonly refer to the organization that registered the domain name with a domain name registrar. Some domain name registries introduce a second-level hierarchy to a TLD that indicates the type of entity intended to register an SLD under it. For example, in the .uk namespace a college or other academic institution would register under the ccSLD, while companies would register under Strictly speaking, domains like and are second level domain themselves, since they are right below a TLD. A list of the official TLDs can be found at and An ordinal-free term to denote domains under which people can register their own domain name is public suffix domain (PSD).

Country-code second-level domains


Main article: .dz § Second-level domains


Main article: .au § Second-level domains


Main article: .at § Second-level domains

In Austria there are two second-level domains available for the public:

The second-level domain


Main article: .br § Second-level domains


Main article: .fr

In France, there are various second-level domains available for certain sectors, including


Main article: .hu

New Zealand

Main article: .nz § Second-level domains


Main article: .pk § Domain categories


Main article: .in § Second-level domains


Main article: .il § Second level domains


Main article: .jp § Second level domains


Main article: .ru § Second-level domains

South Africa

Main article: .za § Second-level domains

South Korea

Main article: .kr § Domains and subdomains


Main article: .es § Second-level domains

Sri Lanka

Main article: .lk § Second-level domains


Main article: .th § Second level domains

Trinidad and Tobago

Main article: .tt


Main article: .tr

In Turkey, domain registrations, including the registration of second-level domains is administrated by[5] There 17 active second-level domains under the .tr TLD.[6] The registration of domains is restricted to Turkish individuals and businesses, or foreign companies with a business activity in Turkey.[7] Second-level domains include for commercial ventures, for academic institutions and for personal use.[8]


Main article: .ua § Second-level domains

Ukraine second-level domains include:

There are also numerous geographic names.

United Kingdom

Main article: .uk § Second-level domains

United States

Main article: .us § States and territories

A two-letter second-level domain is formally reserved for each U.S. state, federal territory, and the District of Columbia.


Main article: .zm § Second-level domains

Historic second-level domains

There are several second-level domains which are no longer available.


Second-level domains under .au which are no longer available include: originally intended for conferences; for the Australian Academic and Research networks; for general information, and for the X.400 mail systems.[9]


Prior to 12 Oct 2010 there were second level domain based on province: — Alberta, — British Columbia, — Manitoba, — New Brunswick, — Newfoundland, — Newfoundland and Labrador, — Nova Scotia, — Northwest Territories, — Nunavut, — Ontario, — Prince Edward Island, — Quebec, — Saskatchewan, — Yukon[citation needed]

Since 2010, some have been replaced (for example, while others have remained under the provincial two letter SLD (e.g., Calgary Board of Education and others were moved to more traditional subdomains ([10]


Historic second-level domains for France included: (for brands), (for commercial use) and [11][12]

The Netherlands

Historic second-level domains for the Netherlands included: (for commercial use)[13][14]


In 2006 the .yu ccTLD was replaced by .rs (for Serbia) and .me (for Montenegro). Second-level domains under .yu included: .ac.yu – for academic institutions, .co.yu for commercial enterprises; .org.yu for organizations and .cg.yu for residents of Montenegro. Only legal entities were allowed to register names under .yu and its second-level domains.[15]


Historic second-level domains for Tuvalu included:

Legal issues

As a result of ICANN's generic top-level domain (gTLD) expansion,[16] the risk of domain squatting has increased significantly. For example, based on current regulations, the registration of the gTLDs .olympics or .redcross is not allowed; however, the registration of sites such as olympics.example or redcross.example is not controlled.[17] Experts say[who?] that further restrictions are needed for second-level domains under the new gTLD .health, as well. For example, second-level domains under or can be easily misused by companies and therefore are a potential threat to Internet users.[18]

See also


  1. ^ "Useful information about domains". Retrieved 29 October 2014.
  2. ^ "Domain registration". Retrieved 29 October 2014.
  3. ^ "Principles and Grants". Retrieved 29 October 2014.
  4. ^ "Sector-based .fr domains". Retrieved 31 October 2014.
  5. ^ "Overview". Retrieved 29 October 2014.
  6. ^ "Who could register which domain name?". Retrieved 29 October 2014.
  7. ^ "Can an individual or a company in abroad register a ".tr" domain name?". Retrieved 29 October 2014.
  8. ^ "Who could register which domain name?". Retrieved 29 October 2014.
  9. ^ "the australian second level domain name system". Retrieved 31 October 2014.
  10. ^ ((cite website|url= November 2017
  11. ^ "Useful information about .fr domains". Retrieved 31 October 2014.
  12. ^ "ICANN-Registrar: French Domains with Accents". Retrieved 31 October 2014.
  13. ^ "Commercial, national & international character with a domain name". Retrieved 25 January 2016.
  14. ^ ".Co.NL WhoIS". Retrieved 25 January 2016.
  15. ^ ".RS - Republic of Serbia .ME - Republic of Montenegro (Former parts of Yugoslavia) Formerly .YU and .CS Country Codes". Retrieved 31 October 2014.
  16. ^ "Delegated strings". Retrieved 29 October 2014.
  17. ^ Easton, Catherine R. (2012). "ICANN's core principles and the expansion of generic top-level domain names". International Journal of Law and Information Technology. 20 (4): 273–290. doi:10.1093/ijlit/eas013.
  18. ^ Mackey, TK; Liang, BA; Kohler, JC; Attaran, A (5 March 2014). "Health Domains for Sale: The Need for Global Health Internet Governance". J Med Internet Res. 16 (3): e62. doi:10.2196/jmir.3276. PMC 3961808. PMID 24598602. Retrieved 2014-10-29.