An SSL certificate is a digital certificate that authenticates the identity of a website and encrypts sensitive information sent to and from that website. It stands for Secure Socket Layer and is used to establish a secure connection between a web server and a web browser. When a website is secured with an SSL certificate, users can be assured that their personal and financial information is protected from being intercepted by third parties. It is often used by websites that handle sensitive information, such as e-commerce sites, banking sites, or sites that require user login credentials.