Secure Sockets Layer (SSL) is a cryptographic protocol that ensures secure communication over the internet. It encrypts the data exchanged between a web server and a browser, preventing hackers from intercepting sensitive information like passwords, credit card details, and personal data. SSL certificates are vital for websites to establish trust with users, as they signal that the site is secure. Websites with SSL encryption display a padlock icon in the browser, reassuring users that their connection is safe and private.