The function epoll() is a system call in the Linux operating system used for monitoring multiple file descriptors to see if they are ready for I/O operations. It is particularly efficient for handling a large number of connections, making it ideal for high-performance network servers. epoll() allows developers to register file descriptors and receive notifications when they become active, reducing the need for constant polling. epoll() operates in two main modes: edge-triggered and level-triggered. In edge-triggered mode, notifications are sent only when a change in the state occurs, while level-triggered mode sends notifications as long as the condition remains true. This flexibility helps optimize resource usage and improve application responsiveness.