What is the method of communication called that uses 2 flags?

The method of communication that uses two flags is called "flag signaling" or "flag semaphore." This system involves positioning the flags in specific angles to represent letters of the alphabet, allowing individuals to convey messages over distances. It is often used in maritime contexts for ship-to-ship communication or signaling to shore. Flag semaphore is an effective way to communicate visually without the need for sound.