The WHOIS service includes WHOIS clients, WHOIS servers, WHOIS data stores, and WHOIS data (domain name registration records). The WHOIS service is not a single centrally-managed data store. Rather, registration data is held in disparate locations and administered by multiple parties that conform to ICANN's standards and conventions for WHOIS service when applicable. For example, Registrars store and provide free, publicly available WHOIS data for the gtld registrations they sponsor that is accessed through a Port 43 service and a web-based service. Registries also provide WHOIS data for registrations in their gTLDs through a Port 43 service and a web-based service. In addition third parties may offer aggregated WHOIS services, sometimes for a fee, that may provide additional functionality and value added services.
When people refer to WHOIS, they may mean several different things. Some mean the WHOIS protocol that specifies the network exchange between a WHOIS client and server, whereas others refer to a perceived or conceptual WHOIS database that registries or registrars support, or to the WHOIS data that registrants provide and ICANN accredited registrars are obliged to make public according to the terms of the Registrar Accreditation Agreement (RAA).