A Domain Name is an identification string that defines a realm of administrative autonomy, authority or control on the Internet. Domain names are formed by the rules and procedures of the Domain Name System (DNS).
Types of Domains
Domain names are organized in subordinate levels (sub-domains) of the DNS root domain. The various levels of domains are :
1.) The first-level set of domain names are the top-level domains (TLDs), including the generic top-level domains (g-TLD's), such as the prominent domains com, net and org, and the country code top-level domains (cc-TLD's).
2.) Below these top-level domains in the DNS hierarchy are the second-level domains (SLD's). These were the domains gov[ernment], edu[cation], com[mercial], mil[itary], org[anisations], net[work] and int[ernational]. As an example, in the domain example.co.uk, co is the second level domain.