Explanation: Distress traffic refers to all radio messages concerning an immediate threat to life or a vessel/aircraft, requiring urgent assistance. This definition, derived from international radio regulations, specifically addresses situations of grave and imminent danger, such as a sinking ship, medical emergency, or man overboard. The primary purpose of distress traffic is to convey critical information to coordinate a rescue or provide necessary aid. Option B is incorrect because "Mayday" is the international *distress signal* used to declare a distress condition and gain immediate attention, but the distress *traffic* encompasses all the subsequent messages containing details about the emergency itself. Option C describes situations typically categorized as *urgency* traffic, signaled by "PAN-PAN." Urgency messages concern the safety of a vessel or persons, or important matters, but do not involve grave and imminent danger to life, which is the hallmark of distress. Option D is too broad; while distress traffic is important and internationally recognized, this definition lacks the critical element of "grave and imminent danger" that defines distress.