An opening on the motherboard where a cicuit board or expansion board can be inserted?

"The circuit board assembly includes an expansion card which is operatively connected to the expansion slot and includes a connector carried on one end thereof. The end of the expansion card having the connector is located adjacent the periphery of the computer case. An extension circuit board is provided and is constructed and arranged to operatively mate with the connector on the expansion card. The extension circuit board extends beyond the periphery of the computer case, and may include multiple ports thereon for connecting peripheral devices to the computer. The extension circuit board is contained within an RF shielding container and is secured to the computer housing."