An SSL certificate is a digital document that helps secure the connection between a user's web browser and a website. It ensures that any data exchanged, like passwords or credit card information, is encrypted and protected from hackers. When a website has an SSL certificate, it shows a padlock icon in the address bar, indicating that the site is safe to use. These certificates are issued by trusted organizations called Certificate Authorities (CAs). They verify the identity of the website owner before issuing the certificate, which helps build trust with visitors. Overall, SSL certificates are essential for maintaining online security and privacy.