An idle timer is a tool used to enhance the security of web applications by automatically logging out users after a period of inactivity, thus protecting sensitive information and improving app performance by reducing unnecessary backend requests. The text describes how to implement an idle session timeout in a React application using the react-idle-timer package, which binds keyboard and mouse events to detect user activity and toggles user idleness based on event triggers. A custom idle detection Hook is created to utilize this package, and the application is structured to prompt users when their session is about to expire, allowing them to either stay logged in or be automatically signed out. This approach ensures that users are notified appropriately about session timeouts, balancing security needs with user experience. The tutorial also highlights the importance of considering the duration of the timeout relative to the risk level of user information and provides steps for setting up the idle timer functionality with examples of how the app behaves with this feature in place.