Busy waiting

In software engineering, busy waiting or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as waiting for keyboard input or waiting for a lock to become available. It can also be used to delay execution for some amount of time; this was necessary on old computers that had no method of waiting a specific length of time other than by repeating a useless loop a specific number of times, but on modern computers with clocks and different processor speeds, this form of time delay is often inaccurate and a sign of a naive attempt at programming. Spinning can be a valid strategy in certain special circumstances, most notably in the implementation of spinlocks within operating systems designed to run on SMP systems. In general, however, it is considered an anti-pattern and should be avoided, as the CPU time spent waiting could have been reassigned to another task.

Reference:
http://en.wikipedia.org/wiki/Busy_waiting