taillight

This term refers specifically to the rear-facing illumination system of a vehicle. While often used interchangeably with "brake light" in casual conversation, a taillight technically remains on whenever the vehicle's headlights are active, whereas a brake light only illuminates during deceleration.

In automotive contexts, the term is typically used in the singular when referring to a specific side of the vehicle (e.g., "the left taillight") and in the plural when discussing the overall lighting system or a general requirement for road safety.