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 upwards 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.