A semaphore may refer to any of the following:
1. A semaphore is a signal that is used to communicate the status of a shared resource. A semaphore is commonly a positive integer from 0 and higher, each value is a different status of that resource.
2. Alternatively referred to as a semaphore telegraph and optical telegraph, a semaphore line is an early form of communication developed by Claude Chappe in 1792. Semaphore line communication works by using visual signaling towers that used blades, paddles, and shutters to signal messages to other visible towers in the area. Using these towers was expensive and could only work in good weather conditions, but it was a much faster method of communicating messages over long distances.