Domain and DNS
A domain is the human-readable name people use to reach a site or send mail. DNS is the public lookup system that maps that name to technical destinations. A DNS record is one published answer; A and AAAA locate hosts, MX routes incoming mail, and NS delegates authority.
Registrar, DNS provider, and authoritative nameserver
The registrar manages the domain registration. A DNS provider hosts its zone records. Authoritative nameservers answer for that zone. These roles can be run by different companies, so an incident may require checking more than one account.
TLS certificate and HTTPS
HTTPS is HTTP carried over an encrypted TLS connection. A TLS certificate helps the browser authenticate the hostname it reached. A valid certificate for one hostname does not automatically cover every subdomain or prove the application itself is safe.
SPF, DKIM, and DMARC
SPF lists approved sending hosts for an envelope domain. DKIM attaches a cryptographic signature to mail. DMARC relates those results to the visible From domain and publishes a policy. Together they support mail authentication, but they cannot guarantee that every fraudulent message is stopped.
Baseline, observation, and incident
A baseline is a reference value against which a later check is compared; it is not a claim of safety. An observation is what a check saw at a particular time and endpoint. An incident is a supported issue that passed the applicable confirmation rule and needs investigation or response.
Verification and recovery
Domain control verification is a DNS TXT or HTTPS challenge showing technical control at a point in time. Recovery is a later observation showing that a supported public signal returned to an acceptable state. Neither term means every part of a business is protected.