Taillight (noun)

1. A red light on the rear of a vehicle that illuminates when the brakes are applied.
2. A light that is located on the back of a vehicle and is used to indicate the vehicle's presence and direction of travel to other drivers.

Origin:

Tail + light.

Examples:

1. He was changing the taillight of his car.
2. The taillights were on indicating the car was stopping.
3. The taillights of the car were not working.
4. The broken taillight was fixed by the mechanic.
5. He was checking the taillights before starting the car.