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.com, 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 .ac.uk ccSLD, while companies would register under .co.uk.
In Austria there are two second-level domains available for the public:
The second-level domain
In France, there are various second-level domains available for certain sectors, including
In Turkey, domain registrations, including the registration of second-level domains is administrated by nic.tr. There 17 active second-level domains under the .tr TLD. The registration of domains is restricted to Turkish individuals and businesses, or foreign companies with a business activity in Turkey. Second-level domains include .com.tr for commercial ventures, .edu.tr for academic institutions and .name.tr for personal use.
Ukraine second-level domains include:
There are also numerous geographic names.
A two-letter second-level domain is formally reserved for each U.S. state, federal territory, and the District of Columbia.
There are several second-level domains which are no longer available.
Second-level domains under .au which are no longer available include: .conf.au originally intended for conferences; .gw.au for the Australian Academic and Research networks; info.au for general information, .otc.au and .telememo.au for the X.400 mail systems.
Prior to 12 Oct 2010 there were second level domain based on province: .ab.ca -- Alberta, .bc.ca -- British Columbia, .mb.ca -- Manitoba, .nb.ca -- New Brunswick, .nf.ca -- Newfoundland, .nl.ca -- Newfoundland and Labrador, .ns.ca -- Nova Scotia, .nt.ca -- Northwest Territories, .nu.ca -- Nunavut, .on.ca -- Ontario, .pe.ca -- Prince Edward Island, .qc.ca -- Quebec, .sk.ca -- Saskatchewan, .yk.ca -- Yukon
Since 2010, some have been replaced (for example, alberta.ca) while others have remained under the provincial two letter SLD (e.g., transport Ontario www.mto.gov.on.ca) while others have been moved to more traditional subdomains (www.transportation.alberta.ca).
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.
Historic second-level domains for Tuvalu included: co.tv
As a result of ICANN's generic top-level domain (gTLD) expansion, 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. Experts say that further restrictions are needed for second-level domains under the new gTLD .health, as well. For example, second-level domains under .tobacco.health or .diet.health can be easily misused by companies and therefore are a potential threat to Internet users.
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