RCU, or Read-Copy Update, is a synchronization mechanism used in computer programming to ensure safe and efficient access to shared data structures. It works by allowing multiple threads to read data simultaneously, while only temporarily blocking access for writing. This allows for increased performance and scalability in multi-threaded applications. RCU is commonly used in operating systems, databases, and other high-performance applications where data access needs to be optimized. It is a powerful tool for managing data consistency and minimizing overhead, making it a valuable tool for developers seeking to improve the performance of their software.