Second-level Domain Definition

A second-level domain is the portion of a domain name directly below the top level domain (TLD) in the domain name system (DNS) hierarchy and the portion that appears immediately to the left of the TLD.

DNS is the network of programs and databases that cooperates to translate domain names to IP addresses. Domain names are user-friendly (i.e., easy to remember) substitutes for IP addresses, which are unique numeric identifiers that are used for addressing on the Internet and other TCP/IP (transmission control protocol/Internet protocol) networks.

In a domain name, the TLD is the last part of the name, that is, the segment furthest to the right. Among the most common are .com, .org and .edu. Two-letter country codes, which are sometimes used after these suffixes, are also TLDs.

Second-level domain names typically provide the name of the organization and/or are descriptive of the service that it provides, as is the case with, for example, the bellevuelinux in

Each second-level domain name must be unique within its TLD and must be registered with the organization (i.e., registry operator) responsible for the TLD to which that name belongs. For example, bellevuelinux is unique within the .org TLD and is registered with the Public Interest Registry.

Created December 1, 2005.
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