Certificate pinning is a cybersecurity technique used to enhance the security of communications between an application and a server. It works by configuring the application to only trust specific digital certificates or public keys when establishing secure connections, such as HTTPS. This prevents attackers from using fraudulent or compromised certificates to impersonate trusted servers, even if a certificate authority is breached. Certificate pinning is commonly used in mobile apps and web applications to protect sensitive data and prevent man-in-the-middle attacks.