What defines a process in an operating system?

A process in an operating system is defined as an application that is actively running on the system. This encompasses not only the program code but also its current activity, which includes values in registers, program counter, and memory allocation. When an application is initiated, the operating system creates a process to manage its execution. This process will have a unique identifier (PID) and resources allocated from the system, allowing for effective scheduling and management by the OS.

Understanding this context helps clarify why the other choices do not accurately represent a process. A stored script waiting to be executed does not create a process until it is actually run; the script itself is simply a file and not an active execution context. A user-triggered action in the background might refer to an execution instance but lacks the comprehensive definition of the entirety of what a process is. Lastly, a physical component of the CPU is unrelated to the concept of a process, as it refers to hardware rather than the software execution context managed by the operating system. Thus, defining a process strictly in terms of an application currently executing on the system captures its essence effectively.