The basic structure of the Domain Name System (DNS) is systematically organized in a hierarchical tree structure that is segregated by a dot.
1st level domain (ccTLD: country code Top-Level Domain): The top-level of the hierarchy, after the root, is often represented by a country code, such as kr, as defined by ISO 3166. The Korea Network Information Center (KRNIC), is the authority that administers the name space for the kr domain.
2nd level domain (SLD: classification, Hangeul domain): The kr domain is further subdivided into a range of second-level domains. There are twelve SLDs classified for specific purposes, as well as one SLD for individuals, and sixteen regional SLDs. Domain names include Hangeul can be registered directly under .kr.
3rd level domain: Registrants can choose any domain name, such as a company name, patent, trademark, etc.. Some words, however, may not be registered, such as reserved or obscene words.