Which term in German refers to 'idle'?

The term in German that best refers to 'idle' is "Leerlauf." This word specifically denotes a state where a machine or mechanism is running without performing useful work or is not engaged in any productive activity, thus capturing the essence of being idle. For example, a vehicle in 'Leerlauf' means that the engine is operating, but the vehicle is not moving.

"Stillstand" translates more closely to 'standstill' or 'halt,' which implies a stoppage rather than a functional idleness. "Inaktiv" means 'inactive' and can describe a lack of activity in a broader sense but does not specifically relate to mechanisms or processes being idle. "Anhalten," on the other hand, means 'to stop' and usually signifies an action taken to cease movement or operation rather than being in an idle state.

Therefore, "Leerlauf" is most accurate in the context of machinery or technical terms when referring to being idle.