A Certificate Authority (CA) is a trusted entity that issues digital certificates, which are used to verify the identity of organizations and individuals online. These certificates play a crucial role in establishing secure connections over the internet, ensuring that data exchanged between users and websites remains private and protected. When a user visits a secure website, their browser checks the site's certificate against a list of trusted CAs. If the certificate is valid and issued by a recognized CA, the browser establishes a secure connection. This process helps prevent fraud and ensures that users can trust the websites they interact with.