Flag semaphore (from the Greek
sema meaning sign and the verb
phero meaning to bear; altogether the sign-bearer) is the
telegraphy system conveying information at a distance by means of visual signals with hand-held flags, rods, disks, paddles, or occasionally bare or gloved hands. Information is encoded by the position of the flags; it is read when the flag is in a fixed position. Semaphores were adopted and widely used (with hand-held flags replacing the mechanical arms of
shutter semaphores) in the maritime world in the 19th century. It is still used during
underway replenishment at sea and is acceptable for emergency communication in daylight or, using lighted wands instead of flags, at night.