The Online Certificate Status Protocol is a way for systems to check whether a certificate has been revoked without relying only on expiration dates.
The Online Certificate Status Protocol, usually called OCSP, is a way for systems to check whether a certificate has been revoked. In plain language, it lets a client ask a trusted responder whether a certificate should still be accepted right now.
OCSP matters because certificates can become unsafe before their expiration date. Systems need some way to learn about revoked certificates instead of assuming that every not-yet-expired certificate is still valid.
It also matters because revocation checking affects how trustworthy a certificate-based connection really is in practice.
OCSP appears in TLS, browser trust checks, enterprise PKI deployments, and certificate-based authentication systems. Teams connect it to Certificate Revocation, Digital Certificate, Certificate Authority, and Public Key Infrastructure.
It is part of the larger question of how trust status is distributed after certificates have already been issued.
When a browser connects to a secure website, it may check whether the site’s certificate has been revoked before fully trusting the connection. That lookup can happen through OCSP or related validation mechanisms.
OCSP is not the same as the certificate itself. The certificate proves identity and trust relationships, while OCSP helps answer whether that certificate is still considered valid.
It is also different from Certificate Revocation as a decision or administrative action. OCSP is a way to communicate revocation status to relying systems.