A foghorn or "fog signal" or "fog bell" is a device that uses sound to warn vehicles of hazards (or of the presence of other vehicles) in foggy conditions. The term is most often used in relation to marine transport. When visual navigation aids such as lighthouses are obscured, foghorns provide an audible warning of rocks, shoals, headlands, or other dangers to shipping.
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foghorn A very loud low-pitched horn, used especially in lighthouses and on large boats.
