PCI / PCI Express / PCI-X Expansion Slots
An expansion slot is a place in a computer where a circuit board or expansion card can be inserted to expand the computer's capabilities. The boards inserted into the expansion slots are called expansion boards, expansion cards, cards, add-ins, and add-ons.
Grundlagen PCI-Express - amdAREA51
Graphics cards are one of the most common devices you plug into PCIe slots. You can also add network cards, SSD expansion cards, sound cards, storage ...
What Are Expansion Slots? - Lifewire
Whether your CPUs, PCIe slots, and expansion cards support PCIe 4.0 speeds is determined by the CPU manufacturer, motherboard manufacturer, and and expansion card manufacturer, respectively.