A Process ID (PID) is a unique numerical identifier assigned by an operating system to each running process. This identifier helps the system manage and track processes, allowing it to allocate resources and schedule tasks efficiently. Each time a new process is created, the operating system assigns it a new PID, ensuring that no two processes have the same identifier at the same time. PIDs are essential for system operations, as they enable users and system administrators to monitor and control processes. For example, commands in command-line interfaces, such as those in Linux or Windows, often require PIDs to terminate or manage specific processes effectively.