subdomain

A subdomain is a domain name that sits under another domain in the DNS hierarchy. Structure: subdomain.example.com, where example.com is the parent and subdomain is the child. You control subdomains through DNS records (typically CNAME or A records) pointed at your own infrastructure or a third party's. They cost nothing—no registration fee, no separate legal entity. This makes subdomains useful for segmenting services: mail.example.com, api.example.com, blog.example.com. But subdomains inherit the parent domain's reputation and risk. If example.com gets seized or flagged, all subdomains go dark with it. For true legal separation and plausible deniability, own a distinct second-level domain. Subdomains are also invisible to WHOIS—you don't register them, so there's no record to enumerate. Useful for operational security if your parent domain is already public. Downside: you're still dependent on the parent domain's registry, registrar, and nameserver infrastructure.