What is the name given to the process of signaling with two flags

Semaphore is a signaling system using two flags (typically held in different positions) to convey messages, especially in maritime and railway communication. The other options (Mutual Exclusion, Deadlock, and Hold & Wait) are concepts in operating system concurrency control related to resource management, not signaling methods. Semaphore signaling is based on the angle and position of flags relative to the signaler's body.