A motherboard (sometimes alternatively known as the; mainboard, system board, planar board, logic board, or colloquially a
mobo) is a printed circuit board (PCB) found in all modern computers which holds many of the crucial components of the system, such as the central processing unit (CPU) and memory, and provides connectors for other peripherals.

Motherboard specifically refers to a PCB with expansion capability - the board is the "mother" of all components attached to it which often include; sound cards, video cards, network cards, hard drives, other forms of persistent storage, TV tuner cards, USB expansion cards, Firewire expansion cards and a variety of other custom components. (The term mainboard is applied to devices with a single board and no additional expansions or capability - in modern terms this would include controlling boards in televisions, washing machines and other embedded systems, which are not true motherboards.