When you connect to a secure website, the server hosting that site presents your browser with something called a "certificate" to verify its identity. This certificate contains identity information, such as the address of the website, which is verified by a third party that your computer trusts. By checking that the address in the certificate matches the address of the website, it is possible to verify that you are securely communicating with the website you intended, and not a third party (such as an attacker on your network).
In this case, the certificate presented to your browser has been revoked by its issuer. This usually means that the integrity of this certificate has been compromised, and that the certificate should not be trusted. You absolutely should not proceed past this point.