It can be anything! An apex, subdomain, or even a URL.
Domain Name: books.nxdt.aiDomain Status: No Object Found>>> Last update of WHOIS database: 2024-09-24T10:21:25.934Z <<<
Domain Name: books.nxdt.ai
Domain Status: No Object Found
>>> Last update of WHOIS database: 2024-09-24T10:21:25.934Z <<<