expansion cards and slots
What is PCIe x1 slot used for? - stc-cable.com
However, PCIe x1 cards can be installed into all PCIe expansion slots, including x4, x8, and x16 PCIe slots. Often people underestimate their role in PCIe x1 slots.
Expansion card - Wikipedia
Expansion slots refer to the additional ports for plugging in extra hardware like graphics cards, solid-state drives, audio cards, and more.
What kind of things, aside from a GPU, can you put into ...
PCIe x1: These are the smallest PCIe slots, used for almost any other cards like average network adapters and USB expansion cards.