An international signal of extreme distress used by ships, planes, and people in life-threatening situations to call for rescue.
Chosen in 1905 for Morse code because it's distinctive and unmistakable: three dots, three dashes, three dots. The letters didn't originally stand for specific words, though people later invented meanings like 'Save Our Souls.'
SOS was brilliant because it looks the same forwards and backwards in Morse code, making it impossible to misunderstand in an emergency. It's one of the few acronyms where the meaning was decided *after* the letters were chosen!
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