This is a frequently asked question in Multi threading interview questions.   A thread pool is simply a set of worker threads, pre-initialized at startup, that can be used to perform tasks and return to the pool when they are finished. This is called pool threads, where a pool of threads of fixed size is created.   By reducing the number of threads in an application and managing their life cycle, the performance problem can be mitigated by thread pooling. Using threads can improve performance and improve system stability. The java.util.concurrent.Executors class typically provides factory methods for creating thread pools.