SSL certificates (Secure Sockets Layer) are small data files that are installed on a web server and activate the HTTPS protocol (Hypertext Transfer Protocol Secure) for secure communication. These certificates encrypt the information exchanged between the user's browser and the server, ensuring that sensitive data is protected against potential attacks and manipulations during transmission. By encryting this data, SSL certificates play a crucial role in maintaining the confidentiality and integrity of information as it travels across the internet, providing a secure and trustworthy online environment for both website owners and their users.