SSL/TLS certificates are digital documents that help secure communication over the internet. They encrypt data exchanged between a user's browser and a website, ensuring that sensitive information, like passwords and credit card numbers, remains private and protected from eavesdroppers. These certificates are issued by trusted entities known as Certificate Authorities (CAs). When a website has a valid SSL/TLS certificate, it displays a padlock icon in the browser's address bar, indicating that the connection is secure. This builds trust with users, as they can be confident that their data is safe while interacting with the site.