An SSL certificate, or Secure Sockets Layer certificate, is a digital certificate that encrypts data transmitted between a user's web browser and a website's server. It ensures that the information exchanged, such as personal details or financial transactions, remains secure and confidential. When a website has an SSL certificate, you'll notice "https://" in the URL, and a padlock icon indicates that the connection is secure. SSL certificates are crucial for safeguarding sensitive data, building trust with users, and improving a website's search engine ranking, as search engines often prioritize secure websites in their results.