What is another term frequently used to refer to the motherboard?

The term "main board" is frequently used to refer to the motherboard because it serves as the primary circuit board in a computer system, connecting all the essential components, such as the CPU, memory, and various expansion cards. The motherboard acts as the central hub for data communication between these components, facilitating their interaction and allowing the system to function as a whole.

The other options refer to different components or concepts within a computer system. A "backplane" is a circuit board that provides the connectors for other boards or devices but does not typically house all system components as the motherboard does. An "expansion card" refers to any additional card that can be inserted into a motherboard to enhance the system's capabilities, such as a graphics or sound card. The term "CPU board" could refer to a circuit board containing the CPU, but it does not encompass other critical components like memory and I/O ports, as the motherboard does. Therefore, "main board" accurately captures the multifaceted role and primary nature of what is commonly understood as the motherboard.