Source : Free On-Line Dictionary of Computing

implicit parallelism
     
         A feature of a programming language for a {parallel
        processing} system which decides automatically which parts to
        run in parallel.
     
        The best way of providing implicit parallelism is still (1995)
        an active research topic.  The problem is to generate the
        right number of parallel tasks of the right size (or
        "{granularity}").  Too many tasks and the system gets bogged
        down in house-keeping, or memory for waiting tasks runs out,
        too few tasks and processors are left idle.
     
        The best performance is usually achieved with {explicit
        parallelism} where the programmer can annotate his program to
        indicate which parts should be executed as independent
        parallel tasks.
     
        (1995-02-16)