What is defined as a set of instructions that can be executed directly by a computer's CPU?

The correct response refers to 'Machine Executable Code' because this term specifically denotes the binary format consisting of instructions that a computer's CPU can execute directly. These instructions are translated from high-level programming languages into a low-level machine language that the CPU understands, allowing the processor to perform operations without needing further interpretation.

'Program Code' encompasses a broader category that includes various forms and languages of code, which may or may not be in a form executable by the CPU. While 'Source Code' refers to human-readable code written in programming languages before it is compiled or assembled into machine code, and an 'Executable File' is a file containing compiled code that is ready to be run but might require an operating system to execute. Therefore, 'Machine Executable Code' is the precise definition relating directly to a set of instructions that the CPU can run instantly.