WHOIS (pronounced "who is"; not an acronym) is a TCP-based query/response protocol which is widely used for querying an official database in order to determine the owner of a domain name, an IP address, or an autonomous system number on the Internet.
WHOIS lookups were traditionally made using a command line interface, but a number of simplified web-based tools now exist for looking up domain ownership details from different databases. Web-based WHOIS clients still rely on the WHOIS protocol to connect to a WHOIS server and do lookups, and command-line WHOIS clients are still quite widely used by system administrators.
