WHOIS (pronounced as the phrase "who is") is a query and response protocol that is widely used for querying databases that store the registered users or assignees of an Internet resource, such as a domain name, an IP address block or an autonomous system, but is also used for a wider range of other information. The protocol stores and delivers database content in a human-readable format. The current iteration of the WHOIS protocol was drafted by the Internet Society, and is documented in RFC 3912.
Whois is also the name of the command-line utility on most UNIX systems used to make WHOIS protocol queries. In addition WHOIS has a sister protocol called Referral Whois (RWhois).