Eventfd is a Linux kernel feature that provides a simple mechanism for event notification between processes or threads. It allows one thread to signal another when an event occurs, using a file descriptor that can be monitored with poll or select. This is particularly useful in scenarios where efficient inter-thread communication is needed without the overhead of more complex synchronization methods. The primary advantage of eventfd is its lightweight nature, making it suitable for high-performance applications. It can be used in various contexts, such as signaling between user-space applications or between kernel and user-space, enhancing the responsiveness and efficiency of concurrent programming.