noun

• (programming) A bit, token, fragment of code, or some other mechanism which is used to restrict access to a shared function or device to a single process at a time, or to synchronize and coordinate events in different processes.
  "The thread increments the semaphore to prevent other threads from entering the critical section at the same time."

verb

• (ambitransitive, figurative) To signal using, or as if using, a semaphore, with the implication that it is done nonverbally.
  "The person intending to Semaphore will make the International Code Signal VOX (I am going to Semaphore to you), and set his Semaphore at the alphabetical sign [...] with the Indicator out, and wait until the person to whom the Semaphore signal is to be made hoists his answering pennant close up. [...] The British method of Semaphoring by flags held in the hand which is shown in plate VIII is exactly the same as the British Movable Semaphore system, which has just been explained, the positions of the apparatus which denote the letters, numbers, and special signs being, it will be seen, identical in each case, and the only difference being in the apparatus employed."