expansion board definition by American Heritage Dictionary
expansion board - Computer Definition
A printed circuit board that plugs into a slot on the motherboard and enables a computer to control a peripheral device. Also called a "card," "interface card," "adapter" or "controller," all the printed circuit boards that plug into a computer's bus are technically expansion boards, because they "expand" the computer's capability. They Used to Be the Norm In earlier PCs, controllers for drives, input/output ports, display, network and sound all resided on plug-in expansion boards. Subsequently, peripheral control was built into the chipset (see PC chipset); however, users still have options to use their own controllers. For example, in order to enhance video game performance, a faster display adapter (graphics card) can be plugged into an empty PCI or PCI Express slot, and the internal display circuit on the motherboard can be disabled. See motherboard. See also bus extender.