What is "Whois"?

In this article:

Whois (pronounced who is) is a protocol that allows you to search databases that store information about domain names. More specifically, it will include information ranging from the creation and expiration date of a domain, the registrar the domain is currently registered through, and the nameservers the domain is using, to the contact information for the registrant and administrator of the domain. There are many sites, including ours, that provide Whois access.