In the Domain Name System (DNS) hierarchy, a second-level domain is a domain that is directly below a top-level domain (TLD). For example, in en.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 or ccTLD registrar. Some TLDs introduce a second-level hierarchy that indicates the type of organization registered under it. For example, in the .uk TLD a college or other academic institution would register under .ac.uk, 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

Domain Name System | Second-level domains

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