A Certificate Authority (CA) is a trusted organization that issues digital certificates, which are used to verify the identity of individuals, organizations, or devices on the internet. These certificates help establish secure connections by enabling encryption and ensuring that the parties involved are who they claim to be. 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, allowing for safe data exchange. This process is essential for online security and trust, especially in transactions involving sensitive information.