The Free On-line Dictionary of Computing (30 December 2018):

tight loop
busy-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)