Conspicuity, signal and identification lights
Conspicuity devices are the lamps and reflectors that make a vehicle conspicuous and visible with respect to its presence, position, direction of travel, change in direction or deceleration. Such lamps may burn steadily, blink, or flash, depending on their intended and regulated function. Most must be fitted in pairs—one left and one right—though some vehicles have multiple pairs (such as two left and two right stop lamps) and/or redundant light sources (such as one left and one right stop lamp, each containing two bulbs).(wikipedia)