C#'s ThreadPool is a system that manages a pool of worker threads for executing tasks concurrently. It allows developers to run multiple operations in the background without manually creating and managing threads, which can be complex and resource-intensive. The ThreadPool automatically allocates threads as needed, improving application performance and responsiveness. When a task is queued to the ThreadPool, it is executed by one of the available threads. This helps optimize resource usage by reusing threads instead of creating new ones for each task. The ThreadPool is particularly useful for short-lived operations, making it a key feature in C# for efficient multitasking.