Domaining Guide

Second-level domain

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Single-letter second-level domains

In the Domain Name System (DNS) hierarchy, a second-level domain (SLD) is a domain that is directly below a top-level domain (TLD). For example, in wikipedia.org, wikipedia is the second-level domain of the .org 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 organization 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.

See also

• Domain Name System
• Top-level domain
• Subdomain
• Country code top-level domain
• Single-letter second-level domains

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Top-level domain
Country code top-level domain
Generic top-level domain
Sponsored top-level domain
List of Internet top-level domains
Proposed top-level domain
Pseudo top-level domain
Second-level domain

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