(en.wikipedia.org) Semaphore - Wikipedia

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Semaphore (lit. 'apparatus for signalling'; from Ancient Greek / σῆμα /(/sêma)/ 'mark, sign, token' and Greek / [[https://en.wiktionary.org/wiki-φόρος#Greek][-φόρος]] (-phóros/)/ 'bearer, carrier') is the use of an apparatus to create a visual signal transmitted over distance. A semaphore can be performed with devices including: fire, lights, flags, sunlight, and moving arms. Semaphores can be used for telegraphy when arranged in visually connected networks, or for traffic signalling such as in railway systems, or traffic lights in cities.