Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
That is correct, its a kind of flag to let one process know what another is doing so they don't interact with common elements or proceed before a result is ready.
For example: if process one is calculating coordinates for a plotter and process two is driving the X & Y motors, if they ran concurrently the motors could move before their final destination was known. A semaphore raised by process one would say "I'm still busy" and process two would look at it to know when it was safe to start moving.