Epoll() is a scalable I/O event notification system used in Linux to efficiently manage multiple file descriptors. It allows applications to monitor multiple streams of input and output, making it ideal for handling numerous simultaneous connections, such as in web servers or network applications. Unlike traditional methods like select() or poll(), epoll() can handle a large number of file descriptors without significant performance degradation. It operates in an event-driven manner, meaning it only notifies the application when a file descriptor is ready for reading or writing, reducing unnecessary CPU usage and improving overall efficiency.