Authentication apps are security tools that help protect your online accounts by generating unique codes. These codes are used in addition to your regular password, adding an extra layer of security. When you log in to a service, the app provides a time-sensitive code that you enter along with your password. Common examples of authentication apps include Google Authenticator and Authy. They work by creating a one-time code based on a shared secret key and the current time. This means even if someone steals your password, they would still need access to your authentication app to log in.