A domain that resides within a higher-level domain in the Domain Name System hierarchy. For example, the domains community.icann.org and gnso.icann.org are subdomains of the second-level domain icann.org. The domain icann.org is a subdomain of the top-level domain .org.
Subdomains can be delegated to specific entities. Registrars, for example, delegate second-level domains to registrants. The registrants can then delegate subdomains within their second-level domains.