The function kqueue() is an event notification interface used in Unix-like operating systems, particularly BSD. It allows applications to efficiently monitor multiple file descriptors to see if they are ready for reading, writing, or have encountered errors. This is particularly useful for servers that handle many simultaneous connections. kqueue() operates by creating a kernel event queue that can register various types of events. When an event occurs, the application can be notified without needing to constantly check each file descriptor, thus improving performance and reducing CPU usage. This makes it a preferred choice for high-performance network applications.