Before moving right to the discussion about the above domains depicted in picture, it is important to know exactly "What is domain name?"
A domain name is an identification string of text that maps to a numeric IP address, used to access a website from client software. For example, the domain name "google.com" points to the IP address. In general, we can say a domain name is the text that a user types into a browser window to reach a particular website. A domain is entered after the protocol in the URL, as shown in the following example.
https://www.google.com/
In this above URL "https" is a protocol, "www" is a subdomain and "google.com" is a domain name.