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).