Any flashing light can be called a blinker, but it usually refers to the turn signal on a car. Before you suddenly turn left, be sure to put your blinker on.
A light that blinks on and off is a blinker, and it may be used to signal your plans to change direction in a car, or to send some kind of signal. Another meaning of the word is "blinder," a kind of eye patch that's used in horse racing to block the horse's peripheral vision so it won't get distracted. To blinker a horse is to attach blinkers to its harness.