General computing term. Also known as thread pooling.
Wikipedia: "By moving such long-running tasks to a worker thread that runs concurrently with the main execution thread, it is possible for the application to remain responsive to user input while executing tasks in the background."
Wikipedia: "…A thread pool maintains multiple threads waiting for tasks to be allocated for concurrent execution by the supervising program. By maintaining a pool of threads, the model increases performance and avoids latency in execution due to frequent creation and destruction of threads for short-lived tasks. The number of available threads is tuned to the computing resources available to the program, such as parallel processors, cores, memory, and network sockets."
See also: multithreading, multicore, and main thread.