running light

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One of several lights on a vehicle, such as a ship, turned on between dusk and dawn to indicate position and size.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun light carried by a boat that indicates the boat's direction; vessels at night carry a red light on the port bow and a green light on the starboard bow