slang A warning light on the dashboard of an automobile meant to alert the driver to a potential problem, such as engine trouble, low fuel, overheating, etc. See? You ignore the idiot light, and the car ends up breaking down in the middle of nowhere.
n. a light (instead of a meter) on a car’s dashboard that indicates the state of various things concerning the operation of the car. (Alludes to these lights’ elimination of the knowledge required to interpret a meter reading, making them suitable for idiots.) I don’t want idiot lights. I want meters!