SSL is the old name of the protocol; every current connection uses its successor, TLS, but the word "SSL certificate" has stuck. The certificate lists the hostnames it is valid for in the Subject Alternative Name field, a validity period, the public key and the certificate authority that issued it. A wildcard entry such as *.example.com covers one level of subdomains.
Browsers trust a certificate if it chains, through one or more intermediate certificates, to a root certificate in their trust store, if the hostname matches, and if the date is inside the validity period. Servers must send the intermediates along with their own certificate; a missing intermediate is a classic cause of errors that appear in some clients and not in others.
Validation levels (DV, OV, EV) describe how much the CA checked about the applicant; the encryption is the same. Maximum lifetimes are being shortened step by step under CA/Browser Forum rules: from 398 days to 200 days in March 2026, then 100 days in 2027 and 47 days in 2029. Automated renewal is the practical approach. A valid certificate shows that the connection is encrypted and that the operator controls the hostname. It says nothing about whether the site's content or owner is trustworthy.
Example
Subject: CN = example.com
SAN: example.com, www.example.com
Issuer: Example CA R3
Valid: 2026-08-01 → 2026-10-30