Networking / Beginners

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Secondary Level Domain (SLD)

Within each ccTLD are secondary level domains (SLD) that serve the same descriptive purpose as the gTLDs. For example, www.leeds.ac.uk is the host www in the leeds domain. The SLD is ac indicating an academic institution, and the gTLD .uk indicates the United Kingdom. The University of Leeds (in the United Kingdom) manages this hostname.

Different ccTLDs define different SLDs, but common secondary domains include the following:

Academic: Universities, colleges, and elementary schools may use ac, acad, ed, or edu.
Commercial: Commercial entities may appear as co or com.
Organization: Noncommercial organizations may use or or org.
Government: Governments may appear as gov or a localized variation. For example, the government of France uses gouv.fr., and Canada uses gc.ca (gc is the Government of Canada).
Military: Military services may appear as mil, mi, or may represent the type of military organization.

Country Code Top Level Domain (ccTLD)

The country code top level domains (ccTLD) allocate domain space to each country. Each domain suffix is a two-letter country code defined by ISO 3166. For example, .uk is the United Kingdom, .jp is Japan, and .us is the United States of America.