Source : Free On-Line Dictionary of Computing

multithreading
     
         Sharing a single {CPU} between multiple tasks (or
        "threads") in a way designed to minimise the time required to
        switch threads.  This is accomplished by sharing as much as
        possible of the program execution environment between the
        different threads so that very little state needs to be saved
        and restored when changing thread.
     
        Multithreading differs from {multitasking} in that threads
        share more of their environment with each other than do tasks
        under multitasking.  Threads may be distinguished only by the
        value of their {program counters} and {stack pointers} while
        sharing a single {address space} and set of {global
        variables}.  There is thus very little protection of one
        thread from another, in contrast to multitasking.
     
        Multithreading can thus be used for very fine-grain
        multitasking, at the level of a few instructions, and so can
        hide {latency} by keeping the processor busy after one thread
        issues a long-latency instruction on which subsequent
        instructions in that thread depend.
     
        A {light-weight process} is somewhere between a thread and a
        full process.
     
        {TL0} is an example of a threaded machine language.
        {Dataflow} computation (E.g. {Id} and {SISAL}) is an extreme
        form of multithreading.
     
        (1997-12-23)