Idle is the term used to characterize the time when a computer’s processor – its CPU – has nothing to do.
An idle state is very similar to that of an automobile: the engine is still running, but it’s not moving the vehicle.
In a computer, the CPU is typically always running, even when it has nothing to do. Depending on the hardware involved, the CPU can enter a “sleep” or low-power state (not to be confused with putting your entire computer to sleep or hibernation). For fractions of a second, the CPU can slow down dramatically or even halt, until it has something to do.
This idle state is often reflected in process monitoring utilities as a faux “Idle” process which reflects the fact that the CPU is doing nothing.
This article needs additional citations for verification. (February 2010)
Idleness is a lack of motion or energy. In describing a person or machine, idle means the act of nothing or no work (for example: "John Smith is an idle person"). This is a person who spends his days doing nothing could be said to be "idly passing his days." (For example: Mary has been idle on her instant messenger account for hours.) A computer processor or communication circuit is described as idle when it is not being used by any program, application or message. Similarly, an engine of an automobile may be described as idle when it is running only to sustain its running (not doing any useful work), this is also called the tickover (see idle).