Real Dictionary

traffic light
Traffic lights are sets of red, amber, and green lights at the places where roads meet. They control the traffic by signalling when vehicles have to stop and when they can go. Traffic lights can also be referred to as a traffic light.

traffic light in American English
a mechanical device consisting of a set of signal lights operating in sequence (usually green to yellow to red and back), placed at intersections to regulate traffic
noun: a set of electrically operated signal lights used to direct or control traffic at intersections

traffic light in British English
noun: one of a set of coloured lights placed at crossroads, junctions, etc, to control the flow of traffic. A red light indicates that traffic must stop and a green light that it may go: usually an amber warning light is added between the red and the green