The "WHOIS" is a database which contains the list of every single domain currently registered in the world.
The most common use of «WHOIS» is for finding information about domain names like legal owner name or expiration date of the domain.
For example, you can find information on a domain (eg: example.am) by querying the «WHOIS» server. All you have to do for that is simply type the domain name in the box above and click the Whois! button.