A unique text name identifying a specific host. Syntactically the domain name contains a sequence of names (tags) separated by dots (.) for example, “www.google.com” – contains top level level domain (com), with second level domain (google) third level domain (www), correspondingly. Note that www subdomain www isn’t frequently used nowadays. Examples of TLDs (top level domains): com – commercial, gov – governmental, edu – educational, org – public organizations, net – telecommunications networks; there are national (usually two characters) TLDs: jp – Japan, fr – France, etc. Separate so called root DNS servers are usually used to support a TLD.