n Any visual signaling system with flags, lights, or mechanically moving arms.
n A visual system for transmitting information by means of two flags that are held one in each hand, using an alphabetic and numeric code based on the position of the signaler’s arms.
n (computing) 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.
v (transitive|intransitive) To signal using (or as if using) a semaphore.