user-defined thread in Java

A user-defined thread is one created by the application developer to accomplish a specific task. All of the applications that we have created up to this point have been multi-threaded, but they contained only one user-defined thread, which calls the main() method. For simplicity, we commonly refer to threads that contain only a single user-defined thread as a single-threaded application, since we are often uninterested in the system threads.