Thread. Parallel thread. Threads are also called command threads (opposite to data threads) or execution threads. A parallel thread is an object executed together with the main application's thread and other parallel threads. The term "parallelism" is considered within the framework of operations systems preemptive multitasking, that is operations systems allocates a certain time slice to a thread and then switches over to another thread. A parallel thread can voluntary give a part of its time slice if it turns into state of waiting for some event. Execution of a thread can be interrupted by a thread with a higher priority.