Universally known as a distress signal sent by ships around the world, SOS is often thought to be an acronym for Save Our Souls.
In point of fact, this etymology is false. Right from the start, the only reason for choosing the Morse code "...- - - ..." (three dots, three dashes, three dots, corresponding to the letters "s", "o" and "s") was because it was easy to memorize, send and decode by potential rescuers. Officially first used in 1905 by German radio, then adopted in 1906 at the International Radiotelegraphic Convention held in Berlin, this signal became effective worldwide on July 1, 1908. One of the first times Marconi telegrapher operators used it, intermixed with the older CQD code, was aboard the Titanic as she sank in the early morning hours of April 15, 1912.
Today, the meaning of SOS in Morse code is so well known that it commonly used to designate any distress signal or call for help.