Derived from the French, venez m'aidez, meaning "come help me" the radio call is given three times in a row ("mayday, mayday, mayday") in emergencies at sea such as fires, a sinking boat, and other life threatening situations. Rescuers are required to take immediate action upon hearing the mayday call. When a mayday call is heard, all radio traffic from potential rescuers (any nearby vessel) is directed toward the emergency. It is considered a criminal act to use the mayday call when there is no evidence of imminent danger or threat to life. In urgent situations where safety isn't an issue, but assistance is necessary, the radio call is "pan-pan, pan-pan, pan-pan" derived from the French, panne, meaning "breakdown".
The term mayday was originated by senior radio officer Frederick Stanley Mockford at Croydon Airport in London in 1923. The airport requested that he come up with a term that could be used on the aircraft radio to denote an emergency. He used the french "m'aider" because the air traffic during that time was predominately between Croydon Airport and Le Bourget Airport in Paris. At a conference in 1948, the term was officially adopted.