Whois (Domain Name Inquiry) contains information about the person and/or organization (company) to which the domain (domain name, e.g. domainadi.com or IP number) belongs. The registration and expiration date of the domain, the name server information of the company where it is hosted are also included.

For example, domainadi.com is a query that shows the name server (ns) information of the hosting company that hosts the domain, whose name the domain is registered under. This type of queries can be made from the addresses below.

In addition, when you want to buy a domain name, you can find out whether the domain has been taken before by querying in this way.

Source: https://tr.wikipedia.org/wiki/Whois