What Is A PCI Slot & For What It Use For?

pci slot A PCIe slot on a motherboard is a physical connector that allows you to add expansion cards to your computer. These slots come in different. There are PCI slot on my cousin's mobo (this from previous post), what it can be used for?

slot 16 login, 300 Mbps Wireless N PCI Express Adapter, PCIe Network Interface Card for Desktop,.