What is a domain name?
A domain name is your identity on the internet.  It’s how people find you or your business. Similar to a street address, a Domain Name or URL (Uniform Resource Locator) is a string of words, numbers, or other signs, separated by dots and used to identify websites and email clients on the internet.  

What is a domain extension?
A domain extension is the part or letters after the last dot, and is called the top level domain, as it helps to classify the purpose of a website or its geographical origin.  The various types of extensions are – TLDs (top level domains), ccTLDs (country code top level domains), and gTLDs (generic top level domains) 

What is a TLD?
A TLD or top-level domain, is the string of letters to the right of the dot (.) such as .com, .org, etc.

Types of TLDs:
gTLD – generic top-level domains; ex: .net, .travel, .mobi etc;
ccTLD – country code top-level domains; ex: .de, .us, .fr, etc.
sTLD – second-level domain; the words/numbers left of the dot; ex: cat.com, abc.net, etc.

What is a domain registry?
A registry is responsible for maintaining the database of names registered with that registry.  The registry receives domain registration information and publishes the information using the WHOIS protocol.

What is Whois?
It is a query and response protocol that is used for querying databases that store the registered users or assignees of an internet resource. example : domain name, an IP address block
The protocol stores and delivers database content in a readable format.

Who is ICANN?
ICANN stands for Internet Corporation for Assigned Names and Numbers.  It was established in 1998 to, as per their definition, defines policies as for how the “names and numbers” of the Internet should run.  ICANN coordinates protocol in how domain names and extensions are managed, routed, allocated, and assigned in order to distinguish each domain as a unique identifier across the global Internet.