Explain Semaphores and how they differ from Mutexes.

A Semaphore maintains a set of permits. Unlike a Mutex (binary), a Counting Semaphore allows a specific number of threads to access a resource.

Mid-level concurrency focuses on coordination patterns. The goal is to move beyond simple 'locks' and use high-level abstractions provided by the language or framework (like Thread Pools) to ensure scalability.