Other forms: Maydays
Mayday is a word that's used around the world as a radio distress signal. When the Coast Guard detects a mayday call, they know a boat is in trouble and needs help.
Mayday is like SOS — it's a word recognized by people who speak a wide variety of languages, and it signifies "I need help!" Mayday calls are mainly used by boat and airplane pilots whose vessels are malfunctioning in some way. If your sailboat is taking on water or your small plane loses an engine, you should say, "Mayday, mayday, mayday!" over your radio. It's from the French m'aider, "help me," which sounds identical to mayday.