Domain Name Structure Levels. Each label to the left specifies a subdivision or subdomain of the domain to the right. Country code top-level domains ccTLD.
TLD gTLD sTLD uTLD ccTLD. A domain name can have any number of levels also known as sub-domains but in practice there are always e or fewer. It is not mandatory nor necessary to have 3 labels to form a domain name.
Org is the top-level icann is the second-level and whois is the third-level.
When entering a domain name into a browser it is normal to omit the dot. In 1985 The Internet Assigned Numbers Authority IANA released six top-level domain names. The domain name structure is a hierarchical structure just like the house address. It consists of two parts the host name and the domain name.