(1) A board that pushes a printed circuit board out of the way of surrounding boards for testing purposes. It plugs into an expansion slot, and the expansion card plugs into the bus extender.
(2) A device that extends the physical distance of a bus. See repeater.
(3) A device that increases the number of expansion slots. It is either an expansion card containing multiple expansion slots, or an expansion card that cables to a separate housing that contains the slots and its own power supply.