a powerful light at the front of a motor vehicle or railway engine.
like a deer (or rabbit) in the headlights
used to refer to a state of fear, panic, or confusion so extreme that it is impossible to act or think normally:faced with too many choices and not enough real information, we are like deer caught in the headlightshis deer-in-the-headlights expression
headlight in other Oxford dictionaries
Definition of headlight in the US English dictionary