What Is an Expansion Card?

An expansion card is a PCB (printed circuit board) that plugs into an expansion slot on a computer motherboard. An expansion card, or add-on card, is used to provide additional functionality to the system or to upgrade an existing function, such as sound or video. For example, an expansion card is a sound card, network card, or dedicated GPU. The most popular expansion slot standard is PCI Express (PCI-e).