The kqueue() function is an event notification interface used in Unix and Linux operating systems. It allows applications to efficiently monitor multiple file descriptors to see if they are ready for reading, writing, or if they have encountered errors. This is particularly useful for servers that need to handle many simultaneous connections without creating a separate thread or process for each one. By using kqueue(), developers can register interest in specific events and receive notifications when those events occur. This helps improve performance and resource management, making it easier to build scalable applications that can handle high loads with minimal overhead.