When an SSL certificate expires, it loses its validity and can no longer be used to secure the connection between the web server and the visitor's browser. This can create security risks, such as exposing sensitive information to hackers or creating an opportunity for a "man-in-the-middle" attack.

When an SSL certificate expires, the website owner can obtain and install a new certificate. As long as the new certificate is installed before the old one expires, the secure connection between the web server and the visitor's browser will be maintained. Therefore, it is important for website owners to monitor the expiration date of their SSL certificate and request a renewal in a timely manner to maintain continuity in the security of their website.