A "task" (real or virtual) found on most-if-not-all multitasking operating systems, which the system runs if it has nothing better to do.  The idle task, which runs at the lowest possible priority, usually does one of the following:

* Runs in an infinite loop,
* Puts the CPU to sleep (especially important for low-power devices; where CPU-sleeping can prolong battery life).

In some systems, the idle task may do useful work; in others, higher-priority tasks are created for any useful background work that needs to be done and the idle task--true to its name--does nothing but idle.

Not named for EricIdle. :)