What best describes the difference between a process and a program?

The best description of the difference between a process and a program is that a process is a subset of a program. A program is a collection of written code that is stored on a disk and represents a set of instructions for the computer to execute. In contrast, a process is an instance of a program that is currently being executed. It contains the program code and its current activity, including the program counter, stack, and variables.

To clarify further, when a program is loaded into memory and executed, it becomes a process. Therefore, every process is derived from a program, making the statement that a process is a subset of a program accurate. It encapsulates the active execution context of the program's instructions at any given moment.

In the context of the other choices, while a running instance of a software application is indeed a process, this description fits a process rather than defining the relationship between a program and a process. The statement regarding resource usage is misleading because a process does not necessarily use more resources than the entire program since the program is dormant until executed. Lastly, a process cannot exist without a corresponding program since the process is fundamentally the execution of that program.