Domain Name Registry Glossary
Clear, plain-language definitions of domain industry concepts, operational protocols, grace period mechanics, and economic concentration metrics used throughout TLD Registry Monitor.
Registry Operator
The legal entity contracted by ICANN to administer a designated top level domain. The registry operator maintains the master authoritative database of all domain registrations within the extension.
ICANN Accredited Registrar
A commercial entity licensed by ICANN and contracted with registry operators to sell domain name registrations, renewals, and transfers directly to registrants or wholesale resellers.
Registry Service Provider (RSP) / Backend
The technical organization operating the core registry software infrastructure: the Shared Registration System (SRS), EPP transactional interfaces, anycast root nameservers, and RDAP directory lookup endpoints.
Extensible Provisioning Protocol (EPP)
The standardized robust XML network protocol (IETF RFC 5730) used by accredited registrars to create, check, renew, transfer, and delete domain names in a registry database.
Add Grace Period (AGP)
A five-calendar-day window immediately following a new domain registration during which the registrar can delete the domain and receive a full credit refund from the registry operator.
Auto-Renew Grace Period (ARGP)
A 45-day window following the expiration of a domain registration during which the registry automatically extends the registration by one year. If the registrant declines renewal, the registrar deletes the domain for a full refund.
Redemption Grace Period (RGP)
A 30-day safety period following non-renewal deletion during which the original registrant may restore their domain name by paying a registry restoration fee before the name is purged.
Herfindahl-Hirschman Index (HHI)
A standardized economic measurement of market concentration calculated as the sum of squared market shares across participating registrars. Values above 2,500 signify highly concentrated retail channels.
Registration Data Access Protocol (RDAP)
The modern RESTful successor protocol to port 43 WHOIS, providing structured JSON responses and authenticated role-based query capabilities for domain ownership records.
De-delegation and Termination
The formal removal of a top-level domain from the authoritative DNS root zone maintained by IANA, causing all second-level registrations under the extension to cease resolving globally.
Root Zone Database
The authoritative master catalog administered by IANA identifying the sponsoring organizations, technical contacts, and designated root nameservers for every delegated top level domain.