The taillight on an automobile.
taillight definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
a light, usually red, at the rear of a vehicle to warn vehicles coming from behind
taillight definition by American Heritage Dictionary
A red light or one of a pair mounted on the rear end of a vehicle. Also called tail lamp.