Mayday is the universal phrase for requesting emergency assistance in a crisis situation on the sea or in the air.
It was first created by Frederick Stanley Mockford, who was a senior radio office trying to figure out a simple distress call sign. As he worked at Croydon Airport, London, and dealt with traffic mainly between England and France, he decided on the word mayday, which is derived from the French words venez m’aider, meaning “come help me”.
Another famous distress call is SOS, or … – – – … in Morse code. It was first used by German radios but then became the worldwide standard in 1906. Although it is often thought to stand for “save our souls”, it is in fact a backronym that was made decades after it came to be. Instead, it was chosen as it is simple to remember (the backronym may have been devised to help people remember the letters) and easy to signal via Morse code. It was most famously used by the RMS Titanic.
The reason why mayday was created (and set as a standard in 1927) was due to the need for a spoken word as the audio radio transmitters were developed.