Which system consists of a publicly available set of databases that contain domain name registration contact information?

WHOIS is a query-and-response protocol standardized in RFC 3912 that provides access to publicly available databases containing domain name registration information, including registrant contact details, name servers, registration dates, and registrar information. It is widely used in security investigations, reconnaissance, and domain ownership verification. The data is maintained by domain registries and accessible through command-line tools, web interfaces, and APIs.

IANA (Internet Assigned Numbers Authority) manages global IP address allocation, DNS root zone, and protocol parameter registries, but is not itself the query database for domain contact information.

CAPTCHA is a challenge-response test used to distinguish humans from automated bots on websites and has no relation to domain registration data.

IETF (Internet Engineering Task Force) is the standards organization that publishes RFCs, including the one defining WHOIS, but it does not operate or host domain registration contact databases.