Source : Free On-Line Dictionary of Computing

expansion card
     
         A circuit board which can be plugged into one of a
        computer's {expansion slots} to provide some optional extra
        facility such as additional {RAM}, {disk controller},
        {coprocessor}, {graphics accelerator}, communication device or
        some special-purpose interface.
     
        Different computers have different standards for the cards
        they accept, e.g. {PCI}.
     
        (1998-06-26)