A set of electronic components fitted to a small piece of plastic that can expand the functionality of your PC. For example, if you want to connect your PC to a network, you will need to add the electronic components that control the way signals are sent over the network cable. This is done by buying a network expansion card. You can fit several expansion cards to a PC by plugging them into an empty expansion slot. To do this, you'll need to open up your PC: you can easily damage the sensitive electronic components, so follow the instructions in your computer's manual.
