What is the difference between a PCIe x16 slot and an express card

What is the difference between a PCIe x16 slot and an express card pcie x16 expansion slot slot card, usb expansion card, pcie riser card, pcie graphics card, graphics card Time Stamp pcie slot configuration gen1 gen2 gen3 PCIe compatibility and performance generates a LOT of confusion In Explaining PCIe Slots

pcie slot configuration gen1 gen2 gen3 In ASUS 「PCIe x16 Slots - 7」

pcie 20 x1 slot So in the first scenario, both physical x16 slots only provide 8 lanes, in the second scenario the first x16 slot provides 16 lanes (for full PCI Express expansion slot of industrial computer, PCI Express cards Physical shape, Signal , x1, x4, x8, x16 x1, x1, ◎, ×, ×, × x4, x1, ◎