The term __________ shall be reserved only to report a lost or trapped firefighter.

The term "MAYDAY" is specifically used in emergency services, particularly in firefighting, to signal that a firefighter is in distress, lost, or trapped. This term is universally recognized among firefighting and rescue personnel as a call for immediate assistance and is critical for ensuring a quick response in life-threatening situations. It conveys urgency and the need for focused attention and resources to locate and rescue the downed firefighter.

Utilizing this specific terminology helps maintain clarity and effectiveness in communication, especially in chaotic environments where time is of the essence. Other terms like "Emergency," "Signal 1," and "Code Red" may refer to various incidents or alerts, but they do not specifically denote the distress of individual firefighters, making "MAYDAY" the most appropriate choice for this scenario.