Source : Free On-Line Dictionary of Computing

tight loop
     
         A {loop} of code that executes without releasing
        any resources to other programs or the {operating system}.
     
        Consider the following pointless {BASIC} loop that counts
        upward indefinitely
     
         10 i = i + 1
         20 GOTO 10
     
        Run on a single-user system such as {MS-DOS} this will not
        cause any problems.  Run on a {cooperative multitasking}
        operating system such as {Windows 3}, the system would appear
        to freeze.
     
        A {pre-emptive multitasking} operating system such as
        {UNIX} or {Windows NT} would "steal" cycles away from
        the program and continue to run other programs.
     
        See also {busy-wait} and {multitasking}.
     
        (1999-05-06)