A circuit board that fits into an expansions slot located on the motherboard . Some adapter boards come installed in the computer, and others may be purchased at a later time to upgrade or add abilities to the computer.
These add-on circuit boards contain the electronic circuitry for many supplemental capabilities, such as a fax modem, and are made to fit a particular type of bus. (Also called expansion cards.)
A plug-in circuit board that adds features to a computer.