Semaphore, Flag

one of the forms of visual communication, based on the transmission of letters, digits, or auxiliary signals by the position or motion of flags held by the signaler; Russian, Latin, and other semaphore alphabets may be used. Flag semaphore can be used to send messages at a rate of 60 to 70 symbols per min over an operating range of approximately 2.5 km. Flags of various colors are used depending on the background. Flag semaphore is used at sea (chiefly by the navy) and by the military on land.